feat: router.back() navigation, read-only evaluation view, auth audit logging

- Convert all Back buttons platform-wide (38 files) to use router.back()
  for natural browser-back behavior regardless of entry point
- Add read-only view for submitted evaluations in closed rounds with
  blue banner, disabled inputs, and contextual back navigation
- Add auth audit logs: MAGIC_LINK_SENT, PASSWORD_RESET_LINK_CLICKED,
  PASSWORD_RESET_LINK_EXPIRED, PASSWORD_RESET_LINK_INVALID
- Learning Hub links navigate in same window for all roles
- Update settings descriptions to reflect all-user scope

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/observer/observer-project-detail.tsx

@@ -2,6 +2,7 @@
 
 import Link from 'next/link'
 import type { Route } from 'next'
+import { useRouter } from 'next/navigation'
 import { trpc } from '@/lib/trpc/client'
 import {
   Card,
@@ -43,6 +44,7 @@ import {
 import { cn, formatDate, formatDateOnly } from '@/lib/utils'
 
 export function ObserverProjectDetail({ projectId }: { projectId: string }) {
+  const router = useRouter()
   const { data, isLoading } = trpc.analytics.getProjectDetail.useQuery(
     { id: projectId },
     { refetchInterval: 30_000 },
@@ -78,8 +80,8 @@ export function ObserverProjectDetail({ projectId }: { projectId: string }) {
           <CardContent className="flex flex-col items-center justify-center py-12 text-center">
             <AlertCircle className="h-12 w-12 text-destructive/50" />
             <p className="mt-2 font-medium">Project Not Found</p>
-            <Button asChild className="mt-4">
-              <Link href={'/observer' as Route}>Back to Dashboard</Link>
+            <Button className="mt-4" onClick={() => router.back()}>
+              Back
             </Button>
           </CardContent>
         </Card>
@@ -152,11 +154,9 @@ export function ObserverProjectDetail({ projectId }: { projectId: string }) {
   return (
     <div className="space-y-6">
       {/* Back button */}
-      <Button variant="ghost" size="sm" className="gap-1.5 -ml-2 text-muted-foreground" asChild>
-        <Link href={'/observer/projects' as Route}>
-          <ArrowLeft className="h-3.5 w-3.5" />
-          Back to Projects
-        </Link>
+      <Button variant="ghost" size="sm" className="gap-1.5 -ml-2 text-muted-foreground" onClick={() => router.back()}>
+        <ArrowLeft className="h-3.5 w-3.5" />
+        Back
       </Button>
 
       {/* Project Header */}