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/src/routes/admin/+layout.svelte

@@ -15,7 +15,8 @@
 		{ href: 'https://analytics.libnovel.cc', label: () => m.admin_nav_analytics() },
 		{ href: 'https://logs.libnovel.cc', label: () => m.admin_nav_logs() },
 		{ href: 'https://uptime.libnovel.cc', label: () => m.admin_nav_uptime() },
-		{ href: 'https://push.libnovel.cc', label: () => m.admin_nav_push() }
+		{ href: 'https://push.libnovel.cc', label: () => m.admin_nav_push() },
+		{ href: 'https://gitea.kalekber.cc/kamil/libnovel', label: () => m.admin_nav_gitea() }
 	];
 
 	interface Props {