feat: live Gitea changelog, Gitea sidebar link, release title/body extraction

- Admin changelog page now fetches releases live from the public Gitea
  API (https://gitea.kalekber.cc) instead of a baked releases.json file
- Remove /static/releases.json from ui/.gitignore (no longer generated)
- Add Gitea to admin sidebar external tools (admin_nav_gitea i18n key,
  all 5 locales, compiled paraglide JS force-added)
- release.yaml: remove 'Fetch releases from Gitea API' step; extract
  release title and body from the tagged commit message for Gitea releases

ui/messages/id.json

@@ -430,5 +430,6 @@
   "feed_reader_label": "membaca",
   "feed_chapters_label": "{n} bab",
   "feed_browse_cta": "Jelajahi katalog",
-  "feed_find_users_cta": "Temukan pembaca"
+  "feed_find_users_cta": "Temukan pembaca",
+  "admin_nav_gitea": "Gitea"
 }