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/lib/i18n/LanguageProvider.tsx

@@ -1,6 +1,6 @@
 'use client'
 
-import { createContext, useContext, useEffect, useState, useCallback, useRef } from 'react'
+import { createContext, useContext, useEffect, useState, useCallback, useRef, useMemo } from 'react'
 import type { ReactNode } from 'react'
 import { SupportedLanguage, loadTranslations, getTranslationValue, Translations } from './load-translations'
 
@@ -97,8 +97,10 @@ export function LanguageProvider({ children, initialLanguage = 'en', initialTran
     return typeof value === 'string' ? value : key
   }, [translations])
 
+  const value = useMemo(() => ({ language, setLanguage, t, translations }), [language, setLanguage, t, translations])
+
   return (
-    <LanguageContext.Provider value={{ language, setLanguage, t, translations }}>
+    <LanguageContext.Provider value={value}>
       {children}
     </LanguageContext.Provider>
   )