feat: fight feed page with filters

Reverse-chronological activity stream of recent fights showing winner,
KO/decision result, arena, sats, and time ago. Filter by tier and bot
name. Click any fight to watch replay. Added to NavBar as FEED link.

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

frontend/src/router.ts

@@ -66,6 +66,11 @@ const routes = [
     name: 'soundboard',
     component: () => import('./pages/SoundboardPage.vue'),
   },
+  {
+    path: '/feed',
+    name: 'feed',
+    component: () => import('./pages/FeedPage.vue'),
+  },
 ]
 
 export const router = createRouter({