fix(notifications): don't resurrect stale toasts on reload

Persisted notifications were restored with their saved 'dismissed' state, so any
that were still active when the page closed came back as active toasts — but
their auto-dismiss timers aren't re-armed on load, leaving them stuck on screen
forever (a burst of errors could pile up dozens). Mark restored entries as
dismissed on load: they stay in the bell history but no longer reappear as live
toasts. The toast surface is session-transient; history persists.

frontend/src/lib/notifications.ts

@@ -118,7 +118,11 @@ function load(): Notification[] {
   try {
     const raw = JSON.parse(localStorage.getItem(HISTORY_KEY) || "[]");
     if (!Array.isArray(raw)) return [];
-    return raw.map((n) => ({ ...n, action: undefined }) as Notification);
+    // Restored entries are history only. Mark them dismissed so they don't
+    // resurrect as active toasts on reload — their auto-dismiss timers aren't
+    // re-armed across a reload, so otherwise they'd stick forever. Also drop the
+    // live `action` callback, which can't survive serialization.
+    return raw.map((n) => ({ ...n, action: undefined, dismissed: true }) as Notification);
   } catch {
     return [];
   }