feat: harden auth, shutdown, and session bundle (0.35.0)

Three features bundled into one release:

- rate-limit /auth/login, /register, /me/password (token bucket,
  5 req/sec sustained with 10-request burst by default; 429 +
  Retry-After header on hit; tracing::warn! per hit so operators
  see attack patterns; AUTH_RATE_PER_SEC / AUTH_RATE_BURST env knobs)
- handle SIGTERM for graceful container stops (replaces bare
  ctrl_c() with a select over ctrl_c + SignalKind::terminate() so
  docker compose stop runs the daemon shutdown path instead of
  letting Chromium leak past SIGKILL)
- clear session.user on 401 from any API call (setOn401Hook in
  api/client.ts, registered from session.svelte.ts gated on
  $app/environment::browser so the SSR bundle never installs it;
  fixes "logged in but no bookmarks/collections" mid-session
  expiry state)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.34.1",
+  "version": "0.35.0",
   "private": true,
   "type": "module",
   "scripts": {