frontend: rebuild bookmark page with drag-and-drop, search, and theme system

- bookmark management with dnd-kit reordering, bulk edit, search,
  category filter/rename, and meta auto-fetch
- migrate /bookmarks → /dashboard/bookmarks under (main) layout
- homepage redesign with category grid, /-key search, dock tooltips
- theme toggle + use-theme, sonner toasts, alert-dialog/skeleton,
  visual refresh of auth pages

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/middleware.ts

@@ -11,7 +11,6 @@ export default auth((req) => {
                      nextUrl.pathname.startsWith("/bind-account");
 
   const isProtected = nextUrl.pathname.startsWith("/dashboard") ||
-                      nextUrl.pathname.startsWith("/bookmarks") ||
                       nextUrl.pathname.startsWith("/admin");
 
   if (isLoggedIn && isAuthPage) {