Replace ticket qty input with +/- buttons, show sold/basket counts

- Entry page shows tickets sold count, remaining, and "in basket" count
- Replace numeric input + Buy button with add-to-basket / +/- controls
- New POST /tickets/adjust/ route creates/cancels tickets to target count
- Keep buy form active after adding (no confirmation replacement)
- New service functions: get_sold_ticket_count, get_user_reserved_count,
  cancel_latest_reserved_ticket

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

bp/tickets/routes.py

@@ -5,6 +5,7 @@ Routes:
   GET  /tickets/              — My tickets list
   GET  /tickets/<code>/       — Ticket detail with QR code
   POST /tickets/buy/          — Purchase tickets for an entry
+  POST /tickets/adjust/       — Adjust ticket quantity (+/-)
 """
 from __future__ import annotations
 
@@ -26,6 +27,9 @@ from .services.tickets import (
     get_user_tickets,
     get_available_ticket_count,
     get_tickets_for_entry,
+    get_sold_ticket_count,
+    get_user_reserved_count,
+    cancel_latest_reserved_ticket,
 )
 
 logger = logging.getLogger(__name__)
@@ -178,4 +182,119 @@ def register() -> Blueprint:
         )
         return await make_response(html, 200)
 
+    @bp.post("/adjust/")
+    @clear_cache(tag="calendars", tag_scope="all")
+    async def adjust_quantity():
+        """
+        Adjust ticket quantity for a calendar entry (+/- pattern).
+        Creates or cancels tickets to reach the target count.
+
+        Form fields:
+          entry_id       — the calendar entry ID
+          ticket_type_id — (optional) specific ticket type
+          count          — target quantity of reserved tickets
+        """
+        form = await request.form
+
+        entry_id_raw = form.get("entry_id", "").strip()
+        if not entry_id_raw:
+            return await make_response("Entry ID required", 400)
+        try:
+            entry_id = int(entry_id_raw)
+        except ValueError:
+            return await make_response("Invalid entry ID", 400)
+
+        # Load entry
+        entry = await g.s.scalar(
+            select(CalendarEntry)
+            .where(
+                CalendarEntry.id == entry_id,
+                CalendarEntry.deleted_at.is_(None),
+            )
+            .options(selectinload(CalendarEntry.ticket_types))
+        )
+        if not entry:
+            return await make_response("Entry not found", 404)
+        if entry.ticket_price is None:
+            return await make_response("Tickets not available for this entry", 400)
+
+        # Ticket type (optional)
+        ticket_type_id = None
+        tt_raw = form.get("ticket_type_id", "").strip()
+        if tt_raw:
+            try:
+                ticket_type_id = int(tt_raw)
+            except ValueError:
+                pass
+
+        target = max(int(form.get("count", 0)), 0)
+        ident = current_cart_identity()
+
+        current = await get_user_reserved_count(
+            g.s, entry_id,
+            user_id=ident["user_id"],
+            session_id=ident["session_id"],
+            ticket_type_id=ticket_type_id,
+        )
+
+        if target > current:
+            # Need to add tickets
+            to_add = target - current
+            available = await get_available_ticket_count(g.s, entry_id)
+            if available is not None and to_add > available:
+                return await make_response(
+                    f"Only {available} ticket(s) remaining", 400
+                )
+            for _ in range(to_add):
+                await create_ticket(
+                    g.s,
+                    entry_id=entry_id,
+                    ticket_type_id=ticket_type_id,
+                    user_id=ident["user_id"],
+                    session_id=ident["session_id"],
+                    state="reserved",
+                )
+        elif target < current:
+            # Need to remove tickets
+            to_remove = current - target
+            for _ in range(to_remove):
+                await cancel_latest_reserved_ticket(
+                    g.s, entry_id,
+                    user_id=ident["user_id"],
+                    session_id=ident["session_id"],
+                    ticket_type_id=ticket_type_id,
+                )
+
+        # Build context for re-rendering the buy form
+        ticket_remaining = await get_available_ticket_count(g.s, entry_id)
+        ticket_sold_count = await get_sold_ticket_count(g.s, entry_id)
+        user_ticket_count = await get_user_reserved_count(
+            g.s, entry_id,
+            user_id=ident["user_id"],
+            session_id=ident["session_id"],
+        )
+
+        # Per-type counts for multi-type entries
+        user_ticket_counts_by_type = {}
+        if entry.ticket_types:
+            for tt in entry.ticket_types:
+                if tt.deleted_at is None:
+                    user_ticket_counts_by_type[tt.id] = await get_user_reserved_count(
+                        g.s, entry_id,
+                        user_id=ident["user_id"],
+                        session_id=ident["session_id"],
+                        ticket_type_id=tt.id,
+                    )
+
+        html = await render_template(
+            "_types/tickets/_adjust_response.html",
+            entry=entry,
+            ticket_remaining=ticket_remaining,
+            ticket_sold_count=ticket_sold_count,
+            user_ticket_count=user_ticket_count,
+            user_ticket_counts_by_type=user_ticket_counts_by_type,
+        )
+
+        return await make_response(html, 200)
+
     return bp