fix: resolve React Error #310 and refactor admin section

- Fix React bug #33580: remove Suspense boundaries co-located with Link components
- Delete settings/loading.tsx and admin/loading.tsx (root cause of race condition)
- Convert all admin navigation from Next.js Link to anchor tags
- Move admin pages to dedicated (admin) route group
- Add AdminHeader matching main header visual design
- Add AdminSidebar with anchor-based navigation
- Add /api/admin/models route handler (replaces server actions for GET)
- Add /api/debug/client-error for server-side browser error reporting
- Add useNoteRefreshOptional() to fix crash in AdminHeader
- Hide Admin Dashboard menu for non-admin users
- Change app icons from yellow to blue (#3A7CA5) matching brand primary
- Fix admin search bar width to match main header

Made-with: Cursor

memento-note/app/(admin)/admin/error.tsx

@@ -0,0 +1,30 @@
+'use client'
+
+import { useEffect } from 'react'
+import { Button } from '@/components/ui/button'
+
+export default function AdminError({
+  error,
+  reset,
+}: {
+  error: Error & { digest?: string }
+  reset: () => void
+}) {
+  useEffect(() => {
+    console.error('Admin route error:', error)
+  }, [error])
+
+  return (
+    <div className="mx-auto max-w-2xl rounded-lg border border-red-200 bg-red-50 p-6 text-red-900 dark:border-red-900 dark:bg-red-950/30 dark:text-red-100">
+      <h2 className="text-lg font-semibold">Une erreur est survenue dans l'administration</h2>
+      <p className="mt-2 text-sm opacity-90">
+        Le rendu de cette page a echoue. Vous pouvez reessayer sans recharger toute l'application.
+      </p>
+      <div className="mt-4">
+        <Button type="button" onClick={reset}>
+          Reessayer
+        </Button>
+      </div>
+    </div>
+  )
+}