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>

bp/calendar_entry/routes.py

@@ -160,10 +160,13 @@ def register():
 
     @bp.context_processor
     async def inject_root():
+        from ..tickets.services.tickets import get_available_ticket_count
+
         view_args = getattr(request, "view_args", {}) or {}
         entry_id = view_args.get("entry_id")
         calendar_entry = None
         entry_posts = []
+        ticket_remaining = None
 
         stmt = (
             select(CalendarEntry)
@@ -185,10 +188,13 @@ def register():
             await g.s.refresh(calendar_entry, ['slot'])
             # Fetch associated posts
             entry_posts = await get_entry_posts(g.s, calendar_entry.id)
+            # Get ticket availability
+            ticket_remaining = await get_available_ticket_count(g.s, calendar_entry.id)
 
         return {
             "entry": calendar_entry,
             "entry_posts": entry_posts,
+            "ticket_remaining": ticket_remaining,
         }        
     @bp.get("/")
     @require_admin