feat: crawler scaffold with chromium launcher (0.22.0)

- crawler module (browser, source trait, jobs, diff) + binary
- chromiumoxide launcher with fetcher feature (auto-downloads
  Chromium on first run, caches under ~/.cache/mangalord/chromium)
- LaunchOptions struct with extra_args, parseable from
  CRAWLER_BROWSER_MODE and CRAWLER_BROWSER_ARGS
- migration 0012 introduces sources, manga_sources,
  chapter_sources, crawler_jobs
- integration tests for headed + headless launch, ipify load+parse,
  and extra-args propagation (all #[ignore], opt-in)

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.21.3",
+  "version": "0.22.0",
   "private": true,
   "type": "module",
   "scripts": {