feat: add location and categories fields, simplify event creation

- 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>

crud.py

@@ -164,6 +164,12 @@ async def purge_unpaid_tickets(event_id: str) -> None:
 
 async def create_event(data: CreateEvent) -> Event:
     event_id = urlsafe_short_hash()
+    # Default end date to start date if not provided
+    if not data.event_end_date:
+        data.event_end_date = data.event_start_date
+    # Default closing date to end date if not provided
+    if not data.closing_date:
+        data.closing_date = data.event_end_date
     event = Event(id=event_id, time=datetime.now(timezone.utc), **data.dict())
     await db.insert("events.events", event)
     return event