chore: beta release v0.5.0-beta

- Bump version to 0.5.0-beta
- Add Apache-2.0 LICENSE (official text) + NOTICE
- Add Docker support: multi-stage Dockerfile + docker-compose
  * non-root user, tini PID 1, gunicorn + uvicorn workers
  * healthcheck, OCI labels, persistent /data volume
- Add GitHub Actions CI (lint/import-check + Docker smoke-test)
- Backend polish:
  * modern lifespan handler (replaces deprecated on_event)
  * explicit sort validation (400 instead of 500)
  * title min_length=1 schema validation
  * configurable data dir + http timeout via env
  * avg_rating helper extracted (DRY)
- Frontend polish:
  * beta badge in title, footer with live version
  * loading spinner on initial fetch
  * updated README, badges, config table, roadmap

app/static/js/app.js

@@ -510,6 +510,15 @@
     $$('[data-close-stats]').forEach(b => b.addEventListener('click', () => { $('#modal-stats').hidden = true; }));
   }
 
+  // Version aus /api/health in den Footer schreiben
+  (async () => {
+    try {
+      const h = await api.get('/api/health');
+      const el = $('#version');
+      if (el && h.version) el.textContent = 'v' + h.version;
+    } catch (_) { /* silent */ }
+  })();
+
   document.addEventListener('DOMContentLoaded', () => {
     wire();
     loadAll();