- Create version.py utility to read version from Docker/VERSION
- Replace hardcoded version '1.0.1' with APP_VERSION from version.py
- Add version logging on FastAPI startup
- Use APP_VERSION in health endpoints and template context
- Add series context helpers: prepare_series_context, get_series_by_key, filter_series_by_missing_episodes
- Update module docstring with identifier convention documentation
- Add unit tests for new series context helper functions
- Update infrastructure.md with template helpers documentation
- Mark Phase 4 (API Layer) as complete