fix: review round 3 — a new tab keeps its account's notices, a revoked tab account lands on the default

Deep-review round 3 over main..improvement/watch-background-audio.

Account boot
- The notification history and settings, and the hints toggle, are read
  when their modules load, which in a new tab (bookmark, typed URL) is
  before BootGate pins the account: they read as nobody's, and the tab's
  first notice replaced the account's stored history (up to 100 entries)
  with a one-item list. They now read again when the tab is pinned
  (onAccountPinned, run by setActiveAccount); a notice raised before the
  pin stays, after the history.
- A tab pinned to an account still in this browser's wallet but whose
  session ended (suspended, deleted, or revoked by "log out everywhere")
  got "signed out" from /api/me while the default account was still
  signed in, and signing in again as anyone else left it there. A refused
  per-tab account now leaves the wallet, and the probe answers as the
  default, so the tab reloads onto it.

Share page (/watch)
- The password unlock is limited per viewer (link + client IP), under a
  per-link ceiling that counts only wrong passwords. Keyed on the link
  alone, ten wrong guesses every five minutes locked out every viewer,
  the ones with the password included. client_ip moves to app.ratelimit
  so the public routes can key on it.
- Its failure messages and the load-failure screen are announced
  (role=alert, the password input described by its error). The sign-in,
  passphrase, password-change and setup form errors get role=alert too.

Comments that still described removed machinery are corrected: App's
collapse flags, SettingsPanel's Save bar, ConfigPanel, authed_format_sig.

Tests: the account's history and hints across the pin; a revoked and a
suspended pinned account; the per-viewer limit and the ceiling; the
limiter's exhausted(); the share page's announced failures; a share
link's feed filters persisted. Each mutation-checked RED for its own
reason.

frontend/src/App.tsx

@@ -111,8 +111,8 @@ export default function App() {
   }
 
   // Collapse state for the two full-height panels (left nav + filter sidebar). Persisted to the
-  // user's preferences (via usePref) so it follows the account across devices; the localStorage mirror
-  // seeds the initial render synchronously so nothing flashes open before the server prefs arrive.
+  // user's preferences (via usePref) so it follows the account across devices, seeded from the `me`
+  // cache at mount; the localStorage mirror covers an account whose server prefs never stored it.
   // Default unpinned (tab + hover-expand overlay); accounts that explicitly pin keep their choice.
   const [filterCollapsed, setFilterCollapsed] = usePref<boolean>("filterCollapsed", true, {
     localKey: LS.filterCollapsed,