feat: tournament bracket UI

TournamentListPage with status filters, TournamentPage with CSS grid
bracket display, lobby view for open tournaments, champion banner,
live polling for active tournaments. Routes at /tournaments and
/tournament/:id. NavBar link added.

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

frontend/src/router.ts

@@ -71,6 +71,16 @@ const routes = [
     name: 'feed',
     component: () => import('./pages/FeedPage.vue'),
   },
+  {
+    path: '/tournaments',
+    name: 'tournaments',
+    component: () => import('./pages/TournamentListPage.vue'),
+  },
+  {
+    path: '/tournament/:id',
+    name: 'tournament',
+    component: () => import('./pages/TournamentPage.vue'),
+  },
 ]
 
 export const router = createRouter({