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/notebook-drag-context.tsx

@@ -1,6 +1,6 @@
 'use client'
 
-import { createContext, useContext, useState, useCallback, ReactNode } from 'react'
+import { createContext, useContext, useState, useCallback, useMemo, ReactNode } from 'react'
 
 interface NotebookDragContextValue {
   draggedNoteId: string | null
@@ -46,18 +46,18 @@ export function NotebookDragProvider({ children }: NotebookDragProviderProps) {
   const isDragging = draggedNoteId !== null
   const isDragOver = dragOverNotebookId !== null
 
+  const value = useMemo(() => ({
+    draggedNoteId,
+    dragOverNotebookId,
+    startDrag,
+    endDrag,
+    dragOver,
+    isDragging,
+    isDragOver,
+  }), [draggedNoteId, dragOverNotebookId, startDrag, endDrag, dragOver, isDragging, isDragOver])
+
   return (
-    <NotebookDragContext.Provider
-      value={{
-        draggedNoteId,
-        dragOverNotebookId,
-        startDrag,
-        endDrag,
-        dragOver,
-        isDragging,
-        isDragOver,
-      }}
-    >
+    <NotebookDragContext.Provider value={value}>
       {children}
     </NotebookDragContext.Provider>
   )