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/lib/api.ts

@@ -22,6 +22,7 @@ export interface Video {
   channel_id: string;
   channel_title: string | null;
   channel_thumbnail: string | null;
+  channel_url: string;
   published_at: string | null;
   thumbnail_url: string | null;
   duration_seconds: number | null;

frontend/src/lib/toast.ts

@@ -0,0 +1,41 @@
+export interface ToastAction {
+  label: string;
+  onClick: () => void;
+}
+export interface ToastItem {
+  id: number;
+  message: string;
+  action?: ToastAction;
+}
+
+let items: ToastItem[] = [];
+let listeners: Array<() => void> = [];
+let counter = 1;
+
+function emit() {
+  listeners.forEach((l) => l());
+}
+
+export function toast(message: string, action?: ToastAction): number {
+  const id = counter++;
+  items = [...items, { id, message, action }];
+  emit();
+  setTimeout(() => dismiss(id), 6000);
+  return id;
+}
+
+export function dismiss(id: number) {
+  items = items.filter((i) => i.id !== id);
+  emit();
+}
+
+export function getToasts(): ToastItem[] {
+  return items;
+}
+
+export function subscribe(listener: () => void): () => void {
+  listeners.push(listener);
+  return () => {
+    listeners = listeners.filter((l) => l !== listener);
+  };
+}