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/app/(admin)/admin/projects/[id]/mentor/page.tsx

@@ -1,7 +1,7 @@
 'use client'
 
 import { Suspense, use, useState } from 'react'
-import Link from 'next/link'
+import { useRouter } from 'next/navigation'
 import { trpc } from '@/lib/trpc/client'
 import { toast } from 'sonner'
 import {
@@ -46,6 +46,7 @@ interface MentorSuggestion {
 }
 
 function MentorAssignmentContent({ projectId }: { projectId: string }) {
+  const router = useRouter()
   const [selectedMentorId, setSelectedMentorId] = useState<string | null>(null)
 
   const utils = trpc.useUtils()
@@ -128,11 +129,9 @@ function MentorAssignmentContent({ projectId }: { projectId: string }) {
     <div className="space-y-6">
       {/* Header */}
       <div className="flex items-center gap-4">
-        <Button variant="ghost" asChild className="-ml-4">
-          <Link href={`/admin/projects/${projectId}`}>
-            <ArrowLeft className="mr-2 h-4 w-4" />
-            Back to Project
-          </Link>
+        <Button variant="ghost" className="-ml-4" onClick={() => router.back()}>
+          <ArrowLeft className="mr-2 h-4 w-4" />
+          Back
         </Button>
       </div>