- Add location (text) and categories (JSON list) to Event model
- Make most CreateEvent fields optional: only title + start date required
- Default end_date to start_date, closing_date to end_date
- Categories stored as JSON text, parsed via validator
- NIP-52 publisher includes location tag and t tags for categories
- Migration m011 adds location and categories columns
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>