feat: Vue SPA as default interface at root URL

- Route `/` now serves the Vue SPA directly (catch-all `/{req}`)
- Legacy Twig interface moved to `/legacy`
- Vue Router base changed from `/vue/` to `/`

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/Controller/MangaController.php

@@ -53,7 +53,7 @@ class MangaController extends AbstractController
         $this->imageManager = new ImageManager(new Driver());
     }
 
-    #[Route('/', name: 'app_manga')]
+    #[Route('/legacy', name: 'app_legacy')]
     public function index(Request $request): Response
     {
         $sort = $request->query->get('sort', 'title');