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/(main)/layout.tsx

@@ -1,3 +1,4 @@
+import { Suspense } from "react";
 import { HeaderWrapper } from "@/components/header-wrapper";
 import { Sidebar } from "@/components/sidebar";
 import { ProvidersWrapper } from "@/components/providers-wrapper";
@@ -28,7 +29,9 @@ export default async function MainLayout({
         {/* Main Layout */}
         <div className="flex flex-1 overflow-hidden">
           {/* Sidebar Navigation - Style Keep */}
-          <Sidebar className="w-64 flex-none flex-col bg-white dark:bg-[#1e2128] border-e border-slate-200 dark:border-slate-800 overflow-y-auto hidden md:flex" user={session?.user} />
+          <Suspense fallback={<div className="w-64 flex-none hidden md:flex" />}>
+            <Sidebar className="w-64 flex-none flex-col bg-white dark:bg-[#1e2128] border-e border-slate-200 dark:border-slate-800 overflow-y-auto hidden md:flex" user={session?.user} />
+          </Suspense>
 
           {/* Main Content Area */}
           <main className="flex min-h-0 flex-1 flex-col overflow-y-auto bg-background-light dark:bg-background-dark p-4 scroll-smooth">