feat: ticket purchase flow, QR display, and admin check-in

Ticket purchase:
- tickets blueprint with routes for my tickets list, ticket detail with QR
- Buy tickets form on entry detail page (HTMX-powered)
- Ticket services: create, query, availability checking

Admin check-in:
- ticket_admin blueprint with dashboard, lookup, and check-in routes
- QR scanner/lookup interface with real-time search
- Per-entry ticket list view
- Check-in transitions ticket state to checked_in

Internal API:
- GET /internal/events/tickets endpoint for cross-app queries
- POST /internal/events/tickets/<code>/checkin for programmatic check-in

Template fixes:
- All templates updated: blog.post.calendars.* → calendars.*
- Removed slug=post.slug parameters (standalone events service)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app.py

@@ -46,6 +46,14 @@ def create_app() -> "Quart":
         url_prefix="/calendars",
     )
 
+    # Tickets blueprint — user-facing ticket views and QR codes
+    from .bp.tickets.routes import register as register_tickets
+    app.register_blueprint(register_tickets())
+
+    # Ticket admin — check-in interface (admin only)
+    from .bp.ticket_admin.routes import register as register_ticket_admin
+    app.register_blueprint(register_ticket_admin())
+
     # Internal API (server-to-server, CSRF-exempt)
     from .events_api import register as register_events_api
     app.register_blueprint(register_events_api())