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/actions/register.ts

@@ -41,11 +41,15 @@ export async function register(prevState: string | undefined, formData: FormData
 
     const hashedPassword = await bcrypt.hash(password, 10);
 
+    const adminEmail = process.env.ADMIN_EMAIL?.toLowerCase();
+    const role = adminEmail && email.toLowerCase() === adminEmail ? 'ADMIN' : 'USER';
+
     await prisma.user.create({
       data: {
         email: email.toLowerCase(),
         password: hashedPassword,
         name,
+        role,
       },
     });