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)/layout.tsx

@@ -0,0 +1,24 @@
+import { AdminProvidersWrapper } from '@/components/admin-providers-wrapper'
+import { detectUserLanguage } from '@/lib/i18n/detect-user-language'
+import { loadTranslations } from '@/lib/i18n/load-translations'
+
+// No <Suspense> here intentionally: combining a Suspense boundary with <Link>
+// components inside the subtree triggers a React production-only bug (React
+// issue #33580, Next.js issue #63388) causing Error #310 "too many re-renders".
+export default async function AdminGroupLayout({
+  children,
+}: {
+  children: React.ReactNode
+}) {
+  const initialLanguage = await detectUserLanguage()
+  const initialTranslations = await loadTranslations(initialLanguage)
+
+  return (
+    <AdminProvidersWrapper
+      initialLanguage={initialLanguage}
+      initialTranslations={initialTranslations}
+    >
+      {children}
+    </AdminProvidersWrapper>
+  )
+}