feat: Mentees & Activity tab on /admin/mentors

Adds a project-centric ops view for mentor management:
- New mentor.getMenteeActivity tRPC procedure aggregates every project
  with wantsMentorship=true and derives a status (unassigned / assigned
  / active / stalled) from the latest message + file activity.
- /admin/mentors becomes a tabbed page: existing Mentor list +
  new Mentees & Activity table with status pills, search, and a
  per-row Assign/Open CTA linking to /admin/projects/[id]/mentor.
- Includes 2 unit tests covering classification + program scoping.

Also: ignore .remember/ (plugin scratch dir).

src/app/(admin)/admin/mentors/page.tsx

@@ -13,6 +13,7 @@ import { Input } from '@/components/ui/input'
 import { Badge } from '@/components/ui/badge'
 import { Button } from '@/components/ui/button'
 import { Skeleton } from '@/components/ui/skeleton'
+import { Tabs, TabsContent, TabsList, TabsTrigger } from '@/components/ui/tabs'
 import {
   Table,
   TableBody,
@@ -21,7 +22,8 @@ import {
   TableHeader,
   TableRow,
 } from '@/components/ui/table'
-import { ArrowUpDown, Search, Users } from 'lucide-react'
+import { ArrowUpDown, GraduationCap, Search, Users } from 'lucide-react'
+import { formatEnumLabel } from '@/lib/utils'
 
 type SortKey = 'name' | 'load' | 'capacity' | 'lastActivity'
 
@@ -37,6 +39,16 @@ function formatRelativePast(date: Date | string | null): string {
   return `${Math.max(0, minutes)}m ago`
 }
 
+const STATUS_BADGE: Record<
+  'unassigned' | 'assigned' | 'active' | 'stalled',
+  { label: string; variant: 'default' | 'secondary' | 'destructive' | 'outline' }
+> = {
+  unassigned: { label: 'Unassigned', variant: 'outline' },
+  assigned: { label: 'Assigned', variant: 'secondary' },
+  active: { label: 'Active', variant: 'default' },
+  stalled: { label: 'Stalled', variant: 'destructive' },
+}
+
 type Mentor = {
   id: string
   name: string | null
@@ -50,7 +62,7 @@ type Mentor = {
   lastActivityAt: Date | string | null
 }
 
-export default function MentorsListPage() {
+function MentorListPanel() {
   const [search, setSearch] = useState('')
   const [sortKey, setSortKey] = useState<SortKey>('load')
   const [sortDir, setSortDir] = useState<'asc' | 'desc'>('asc')
@@ -128,21 +140,6 @@ export default function MentorsListPage() {
 
   return (
     <div className="space-y-6">
-      <div className="flex items-center justify-between">
-        <div>
-          <h1 className="text-2xl font-semibold tracking-tight">Mentors</h1>
-          <p className="text-muted-foreground">
-            All users with the MENTOR role and their current workload.
-          </p>
-        </div>
-        <Button asChild variant="outline">
-          <Link href="/admin/members">
-            <Users className="mr-2 h-4 w-4" />
-            Manage Members
-          </Link>
-        </Button>
-      </div>
-
       <div className="grid gap-4 md:grid-cols-3">
         <Card>
           <CardHeader className="pb-2">
@@ -279,3 +276,252 @@ export default function MentorsListPage() {
     </div>
   )
 }
+
+type StatusFilter = 'all' | 'unassigned' | 'assigned' | 'active' | 'stalled'
+
+function MenteeActivityPanel() {
+  const [search, setSearch] = useState('')
+  const [statusFilter, setStatusFilter] = useState<StatusFilter>('all')
+
+  const { data, isLoading } = trpc.mentor.getMenteeActivity.useQuery({})
+
+  const filtered = useMemo(() => {
+    if (!data) return []
+    const q = search.trim().toLowerCase()
+    return data.rows.filter((r) => {
+      if (statusFilter !== 'all' && r.status !== statusFilter) return false
+      if (!q) return true
+      const hay = [
+        r.project.title,
+        r.project.country ?? '',
+        r.teamLead?.name ?? '',
+        r.teamLead?.email ?? '',
+        r.mentor?.name ?? '',
+        r.mentor?.email ?? '',
+      ]
+        .join(' ')
+        .toLowerCase()
+      return hay.includes(q)
+    })
+  }, [data, search, statusFilter])
+
+  const totals = data?.totals ?? { unassigned: 0, assigned: 0, active: 0, stalled: 0 }
+
+  const StatusPill = ({ value, label, count }: { value: StatusFilter; label: string; count: number }) => (
+    <button
+      type="button"
+      onClick={() => setStatusFilter(value)}
+      className={`rounded-md border px-2.5 py-1 text-xs font-medium transition-colors ${
+        statusFilter === value
+          ? 'bg-primary text-primary-foreground border-primary'
+          : 'bg-background hover:bg-muted'
+      }`}
+    >
+      {label} <span className="tabular-nums opacity-80">({count})</span>
+    </button>
+  )
+
+  return (
+    <div className="space-y-6">
+      <div className="grid gap-4 md:grid-cols-4">
+        <Card>
+          <CardHeader className="pb-2">
+            <CardTitle className="text-muted-foreground text-xs font-medium uppercase tracking-wide">
+              Unassigned
+            </CardTitle>
+          </CardHeader>
+          <CardContent>
+            <div className="text-3xl font-bold tabular-nums">{totals.unassigned}</div>
+          </CardContent>
+        </Card>
+        <Card>
+          <CardHeader className="pb-2">
+            <CardTitle className="text-muted-foreground text-xs font-medium uppercase tracking-wide">
+              Assigned
+            </CardTitle>
+          </CardHeader>
+          <CardContent>
+            <div className="text-3xl font-bold tabular-nums">{totals.assigned}</div>
+          </CardContent>
+        </Card>
+        <Card>
+          <CardHeader className="pb-2">
+            <CardTitle className="text-muted-foreground text-xs font-medium uppercase tracking-wide">
+              Active
+            </CardTitle>
+          </CardHeader>
+          <CardContent>
+            <div className="text-3xl font-bold tabular-nums">{totals.active}</div>
+          </CardContent>
+        </Card>
+        <Card>
+          <CardHeader className="pb-2">
+            <CardTitle className="text-muted-foreground text-xs font-medium uppercase tracking-wide">
+              Stalled
+            </CardTitle>
+          </CardHeader>
+          <CardContent>
+            <div className="text-3xl font-bold tabular-nums text-destructive">
+              {totals.stalled}
+            </div>
+          </CardContent>
+        </Card>
+      </div>
+
+      <Card>
+        <CardHeader className="space-y-4">
+          <div className="flex items-center justify-between gap-4">
+            <CardTitle className="text-base">Mentee teams</CardTitle>
+            <div className="flex flex-wrap gap-1.5">
+              <StatusPill
+                value="all"
+                label="All"
+                count={
+                  totals.unassigned + totals.assigned + totals.active + totals.stalled
+                }
+              />
+              <StatusPill value="unassigned" label="Unassigned" count={totals.unassigned} />
+              <StatusPill value="assigned" label="Assigned" count={totals.assigned} />
+              <StatusPill value="active" label="Active" count={totals.active} />
+              <StatusPill value="stalled" label="Stalled" count={totals.stalled} />
+            </div>
+          </div>
+          <div className="relative">
+            <Search className="text-muted-foreground absolute left-3 top-1/2 h-4 w-4 -translate-y-1/2" />
+            <Input
+              value={search}
+              onChange={(e) => setSearch(e.target.value)}
+              placeholder="Search by project, team lead, or mentor…"
+              className="pl-9"
+            />
+          </div>
+        </CardHeader>
+        <CardContent>
+          {isLoading ? (
+            <div className="space-y-2">
+              {[1, 2, 3, 4, 5].map((i) => (
+                <Skeleton key={i} className="h-14 w-full" />
+              ))}
+            </div>
+          ) : filtered.length === 0 ? (
+            <div className="text-muted-foreground py-12 text-center text-sm">
+              {search || statusFilter !== 'all'
+                ? 'No matching teams.'
+                : 'No teams have requested mentorship yet.'}
+            </div>
+          ) : (
+            <div className="overflow-hidden rounded-md border">
+              <Table>
+                <TableHeader>
+                  <TableRow>
+                    <TableHead>Project</TableHead>
+                    <TableHead>Status</TableHead>
+                    <TableHead>Mentor</TableHead>
+                    <TableHead className="text-right">Messages</TableHead>
+                    <TableHead className="text-right">Files</TableHead>
+                    <TableHead>Last activity</TableHead>
+                    <TableHead></TableHead>
+                  </TableRow>
+                </TableHeader>
+                <TableBody>
+                  {filtered.map((r) => {
+                    const badge = STATUS_BADGE[r.status]
+                    return (
+                      <TableRow key={r.project.id}>
+                        <TableCell>
+                          <div className="font-medium">{r.project.title}</div>
+                          <div className="text-muted-foreground text-xs">
+                            {r.teamLead?.name ?? r.teamLead?.email ?? '—'}
+                            {r.project.oceanIssue && (
+                              <>
+                                {' · '}
+                                {formatEnumLabel(r.project.oceanIssue)}
+                              </>
+                            )}
+                          </div>
+                        </TableCell>
+                        <TableCell>
+                          <Badge variant={badge.variant} className="text-xs">
+                            {badge.label}
+                          </Badge>
+                        </TableCell>
+                        <TableCell>
+                          {r.mentor ? (
+                            <div className="text-sm">
+                              <div>{r.mentor.name ?? r.mentor.email}</div>
+                              <div className="text-muted-foreground text-xs tabular-nums">
+                                {r.mentor.currentLoad}
+                                {r.mentor.maxAssignments != null
+                                  ? `/${r.mentor.maxAssignments}`
+                                  : ''}
+                                {' load'}
+                              </div>
+                            </div>
+                          ) : (
+                            <span className="text-muted-foreground text-sm">—</span>
+                          )}
+                        </TableCell>
+                        <TableCell className="text-right tabular-nums">
+                          {r.messageCount}
+                        </TableCell>
+                        <TableCell className="text-right tabular-nums">{r.fileCount}</TableCell>
+                        <TableCell className="text-sm">
+                          {formatRelativePast(r.lastActivityAt as unknown as Date | null)}
+                        </TableCell>
+                        <TableCell className="text-right">
+                          <Button asChild size="sm" variant="outline">
+                            <Link href={`/admin/projects/${r.project.id}/mentor`}>
+                              {r.mentor ? 'Open' : 'Assign'}
+                            </Link>
+                          </Button>
+                        </TableCell>
+                      </TableRow>
+                    )
+                  })}
+                </TableBody>
+              </Table>
+            </div>
+          )}
+        </CardContent>
+      </Card>
+    </div>
+  )
+}
+
+export default function MentorsListPage() {
+  return (
+    <div className="space-y-6">
+      <div className="flex items-center justify-between">
+        <div>
+          <h1 className="text-2xl font-semibold tracking-tight">Mentors</h1>
+          <p className="text-muted-foreground">
+            Manage the mentor pool and track mentee teams across the program.
+          </p>
+        </div>
+        <Button asChild variant="outline">
+          <Link href="/admin/members">
+            <Users className="mr-2 h-4 w-4" />
+            Manage Members
+          </Link>
+        </Button>
+      </div>
+
+      <Tabs defaultValue="mentors" className="space-y-6">
+        <TabsList>
+          <TabsTrigger value="mentors">
+            <GraduationCap className="mr-2 h-4 w-4" /> Mentors
+          </TabsTrigger>
+          <TabsTrigger value="mentees">
+            <Users className="mr-2 h-4 w-4" /> Mentees & Activity
+          </TabsTrigger>
+        </TabsList>
+        <TabsContent value="mentors">
+          <MentorListPanel />
+        </TabsContent>
+        <TabsContent value="mentees">
+          <MenteeActivityPanel />
+        </TabsContent>
+      </Tabs>
+    </div>
+  )
+}