feat: mentor detail side sheet + Teams column

The mentor list now ends with a Teams column showing chips of each
mentor's active assignments (truncated at 2 + overflow badge). Clicking
any row opens a right-side Sheet with the mentor's profile (expertise,
country, joined date, max assignments) and a per-team activity feed —
project, status (active / completed / dropped), assignment date, and
counts of messages / files / milestones with their last timestamp.

Stat cards on both the Mentor and Mentee panels were stale and not
particularly informative, so they're gone — the table itself is now
the focal element on each panel.

getMentorPool gained an activeTeams[] field; new getMentorDetail query
backs the side sheet.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/server/routers/mentor.ts

@@ -1016,6 +1016,7 @@ export const mentorRouter = router({
             },
             select: {
               completionStatus: true,
+              project: { select: { id: true, title: true } },
               messages: {
                 orderBy: { createdAt: 'desc' },
                 take: 1,
@@ -1043,9 +1044,14 @@ export const mentorRouter = router({
         let current = 0
         let completed = 0
         const activityDates: Date[] = []
+        const activeTeams: { id: string; title: string }[] = []
         for (const a of m.mentorAssignments) {
-          if (a.completionStatus === 'completed') completed++
-          else current++
+          if (a.completionStatus === 'completed') {
+            completed++
+          } else {
+            current++
+            activeTeams.push(a.project)
+          }
           if (a.messages[0]) activityDates.push(a.messages[0].createdAt)
           if (a.files[0]) activityDates.push(a.files[0].createdAt)
           if (a.milestoneCompletions[0])
@@ -1069,6 +1075,7 @@ export const mentorRouter = router({
           maxAssignments: m.maxAssignments,
           capacityRemaining,
           lastActivityAt,
+          activeTeams,
         }
       })
 
@@ -2305,4 +2312,81 @@ export const mentorRouter = router({
       })
       return dropped
     }),
+
+  /**
+   * Per-mentor activity detail used by the admin mentor side sheet. For each
+   * (active or dropped) assignment, returns the project, key timestamps, and
+   * counts of messages, files, and completed milestones so the admin can see
+   * "what has this mentor been up to" at a glance.
+   */
+  getMentorDetail: adminProcedure
+    .input(z.object({ mentorId: z.string() }))
+    .query(async ({ ctx, input }) => {
+      const mentor = await ctx.prisma.user.findUniqueOrThrow({
+        where: { id: input.mentorId },
+        select: {
+          id: true,
+          name: true,
+          email: true,
+          country: true,
+          expertiseTags: true,
+          maxAssignments: true,
+          createdAt: true,
+        },
+      })
+
+      const assignments = await ctx.prisma.mentorAssignment.findMany({
+        where: { mentorId: input.mentorId },
+        orderBy: { assignedAt: 'desc' },
+        include: {
+          project: {
+            select: {
+              id: true,
+              title: true,
+              competitionCategory: true,
+              country: true,
+            },
+          },
+          _count: {
+            select: { messages: true, files: true, milestoneCompletions: true },
+          },
+          messages: {
+            orderBy: { createdAt: 'desc' },
+            take: 1,
+            select: { createdAt: true },
+          },
+          files: {
+            orderBy: { createdAt: 'desc' },
+            take: 1,
+            select: { createdAt: true },
+          },
+          milestoneCompletions: {
+            orderBy: { completedAt: 'desc' },
+            take: 1,
+            select: { completedAt: true },
+          },
+        },
+      })
+
+      return {
+        mentor,
+        assignments: assignments.map((a) => ({
+          id: a.id,
+          assignedAt: a.assignedAt,
+          method: a.method,
+          completionStatus: a.completionStatus,
+          droppedAt: a.droppedAt,
+          droppedReason: a.droppedReason,
+          droppedBy: a.droppedBy,
+          workspaceEnabled: a.workspaceEnabled,
+          project: a.project,
+          messageCount: a._count.messages,
+          fileCount: a._count.files,
+          milestoneCompletionCount: a._count.milestoneCompletions,
+          lastMessageAt: a.messages[0]?.createdAt ?? null,
+          lastFileAt: a.files[0]?.createdAt ?? null,
+          lastMilestoneAt: a.milestoneCompletions[0]?.completedAt ?? null,
+        })),
+      }
+    }),
 })