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/learning/new/page.tsx

@@ -2,7 +2,6 @@
 
 import { useCallback, useEffect, useState } from 'react'
 import { useRouter } from 'next/navigation'
-import Link from 'next/link'
 import dynamic from 'next/dynamic'
 import { trpc } from '@/lib/trpc/client'
 import { Button } from '@/components/ui/button'
@@ -165,11 +164,9 @@ export default function NewLearningResourcePage() {
     <div className="flex min-h-screen flex-col">
       {/* Sticky toolbar */}
       <div className="sticky top-0 z-30 flex items-center justify-between border-b bg-background/95 px-4 py-2 backdrop-blur supports-[backdrop-filter]:bg-background/60">
-        <Button variant="ghost" size="sm" asChild>
-          <Link href="/admin/learning">
-            <ArrowLeft className="mr-2 h-4 w-4" />
-            Back
-          </Link>
+        <Button variant="ghost" size="sm" onClick={() => router.back()}>
+          <ArrowLeft className="mr-2 h-4 w-4" />
+          Back
         </Button>
 
         <div className="flex items-center gap-2">