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/context/NoteRefreshContext.tsx

@@ -1,6 +1,6 @@
 'use client'
 
-import { createContext, useContext, useState, useCallback } from 'react'
+import { createContext, useContext, useState, useCallback, useMemo } from 'react'
 
 interface NoteRefreshContextType {
   refreshKey: number
@@ -16,8 +16,10 @@ export function NoteRefreshProvider({ children }: { children: React.ReactNode })
     setRefreshKey(prev => prev + 1)
   }, [])
 
+  const value = useMemo(() => ({ refreshKey, triggerRefresh }), [refreshKey, triggerRefresh])
+
   return (
-    <NoteRefreshContext.Provider value={{ refreshKey, triggerRefresh }}>
+    <NoteRefreshContext.Provider value={value}>
       {children}
     </NoteRefreshContext.Provider>
   )
@@ -30,3 +32,12 @@ export function useNoteRefresh() {
   }
   return context
 }
+
+/**
+ * Same as useNoteRefresh but tolerates being called outside the provider
+ * (e.g. shared header rendered in admin pages). Returns a no-op when absent.
+ */
+export function useNoteRefreshOptional(): NoteRefreshContextType {
+  const context = useContext(NoteRefreshContext)
+  return context ?? { refreshKey: 0, triggerRefresh: () => {} }
+}