feat: add user_id ticket support and public events endpoint

- Tickets can be created with user_id instead of name/email
- name/email default to empty string in DB (not NULL-safe)
- New endpoints: GET /api/v1/events/public, GET /api/v1/tickets/user/{user_id}
- POST /api/v1/tickets/{event_id} accepts user_id in body
- Migration m007 adds user_id column to tickets table
- CreateTicket validates: either user_id or (name + email) required

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

migrations.py

@@ -175,3 +175,11 @@ async def m006_add_extra_fields(db):
 
     # Add 'extra' column to ticket table
     await db.execute("ALTER TABLE events.ticket ADD COLUMN extra TEXT;")
+
+
+async def m007_add_user_id(db):
+    """
+    Add user_id column to tickets table.
+    Allows ticket purchase via LNbits user-id without name/email.
+    """
+    await db.execute("ALTER TABLE events.ticket ADD COLUMN user_id TEXT;")