fix(ui): notification UX — outside-click close, toast countdown, hide entry actions

- NotificationCenter closes on outside click (document listener, not an overlay
  that the blurred header trapped) and no longer needs a second bell click.
- Toasts show a level-colored countdown bar and auto-dismiss faster (6s default).
- Hidden-video notifications carry structured meta so the center offers an in-app
  'Find in feed' (jump to that channel's hidden videos) and a one-click 'Unhide',
  working even after a reload when the live Undo callback is gone.

frontend/src/lib/notifications.ts

@@ -10,13 +10,25 @@ export interface NotifAction {
   onClick: () => void;
 }
 
+// Structured payload that lets the Notification Center offer in-app actions even
+// after a reload (when live `action` callbacks are gone).
+export type NotifMeta = {
+  kind: "video-hidden";
+  videoId: string;
+  title: string;
+  channelId: string;
+  channelName: string;
+};
+
 export interface Notification {
   id: number;
   level: NotifLevel;
   title?: string;
   message: string;
   action?: NotifAction;
+  meta?: NotifMeta;
   requiresInteraction: boolean;
+  duration?: number; // auto-dismiss ms (undefined when it stays until acted on)
   ts: number;
   read: boolean;
   dismissed: boolean; // transient toast surface closed (still kept in history)
@@ -27,12 +39,13 @@ export interface NotifyInput {
   level?: NotifLevel;
   title?: string;
   action?: NotifAction;
+  meta?: NotifMeta;
   requiresInteraction?: boolean;
 }
 
 const HISTORY_KEY = "subfeed.notifications";
 const MAX_HISTORY = 100;
-const DEFAULT_TTL = 9000;
+const DEFAULT_TTL = 6000;
 const ERROR_TTL = 15000;
 
 let items: Notification[] = load();
@@ -90,6 +103,11 @@ export function notify(input: NotifyInput): number {
   const id = counter++;
   const requiresInteraction = input.requiresInteraction ?? false;
   const level = input.level ?? "info";
+  const duration = requiresInteraction
+    ? undefined
+    : level === "error" || level === "fatal"
+      ? ERROR_TTL
+      : DEFAULT_TTL;
   items = [
     ...items,
     {
@@ -98,17 +116,16 @@ export function notify(input: NotifyInput): number {
       title: input.title,
       message: input.message,
       action: input.action,
+      meta: input.meta,
       requiresInteraction,
+      duration,
       ts: Date.now(),
       read: false,
       dismissed: false,
     },
   ];
   emit();
-  if (!requiresInteraction) {
-    const ttl = level === "error" || level === "fatal" ? ERROR_TTL : DEFAULT_TTL;
-    setTimeout(() => dismiss(id), ttl);
-  }
+  if (duration) setTimeout(() => dismiss(id), duration);
   return id;
 }