fc3e: PostsView + /posts route — IntersectionObserver infinite scroll, URL-driven filters

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/router.js

@@ -9,6 +9,7 @@ import SeriesReaderView from './views/SeriesReaderView.vue'
 import SubscriptionsView from './views/SubscriptionsView.vue'
 import CredentialsView from './views/CredentialsView.vue'
 import DownloadsView from './views/DownloadsView.vue'
+import PostsView from './views/PostsView.vue'
 
 // The application's front door. `/` redirects here. Changing the front door
 // is a one-line edit (e.g. '/gallery' or '/tags').
@@ -31,6 +32,7 @@ const routes = [
   { path: '/settings', name: 'settings', component: SettingsView, meta: { title: 'Settings' } },
 
   // FC-3: subscription backbone
+  { path: '/posts',         name: 'posts',         component: PostsView,         meta: { title: 'Posts'         } },
   { path: '/subscriptions', name: 'subscriptions', component: SubscriptionsView, meta: { title: 'Subscriptions' } },
   { path: '/credentials',   name: 'credentials',   component: CredentialsView,   meta: { title: 'Credentials'   } },
   { path: '/downloads',     name: 'downloads',     component: DownloadsView,     meta: { title: 'Downloads'     } }