fix: address reader-UI feedback (shorts, search, tags, login, UX)

- Shorts: confirm via youtube.com/shorts/<id> probe (SOCS cookie bypasses the
  consent redirect) instead of a 60s heuristic; concurrent probing, shorts_probed
  flag, scheduled refinement (migration 0005)
- Search: match title + channel name only (descriptions caused noisy results)
- Faceted tag filtering: AND across categories (language AND topic narrows),
  OR within a category; any/all toggle applies to topics
- Language detection: majority vote over individual titles (fixes misdetections
  like multipoleguy -> English; drops bogus Polish/Romanian)
- Login: drop forced consent so returning sign-in is quick (select_account)
- Feed cards: clickable channel name (opens channel), persistent saved badge,
  undo toast on hide, Hidden view to restore; tag chips show counts in tooltip

frontend/src/App.tsx

@@ -12,6 +12,7 @@ import Login from "./components/Login";
 import Header from "./components/Header";
 import Sidebar from "./components/Sidebar";
 import Feed from "./components/Feed";
+import Toaster from "./components/Toaster";
 
 const DEFAULT_FILTERS: FeedFilters = {
   tags: [],
@@ -83,6 +84,7 @@ export default function App() {
           <Feed filters={filters} view={view} />
         </main>
       </div>
+      <Toaster />
     </div>
   );
 }