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

.dockerignore

@@ -0,0 +1,45 @@
+# Ausgeschlossene Pfade und Dateien fuer Docker-Build-Kontext.
+# Identisch zu .gitignore, plus build-spezifische Ausnahmen.
+
+# Python
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+.Python
+venv/
+.venv/
+env/
+.pytest_cache/
+.mypy_cache/
+.ruff_cache/
+
+# IDE
+.vscode/
+.idea/
+*.swp
+*.swo
+.DS_Store
+
+# App data (lokal generiert, NICHT in den Container)
+data/*.db
+data/*.db-journal
+data/*.db-wal
+data/*.db-shm
+data/backups/
+data/exports/
+
+# Logs
+*.log
+logs/
+
+# Secrets / Env
+.env
+.env.local
+*.pem
+
+# Docker-Artefakte
+Dockerfile
+.dockerignore
+docker-compose.yml
+.docker/