Add page-local ticket adjust route that returns HX-Refresh

The cards were posting to tickets.adjust_quantity which returns the
entry detail buy form — wrong context for the page summary. New
page_summary.adjust_ticket route calls the service and returns
HX-Refresh: true so the whole listing refreshes with correct counts.

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

bp/page/routes.py

@@ -3,8 +3,9 @@ Page summary blueprint — shows upcoming events across all calendars
 for a container (e.g. the village hall).
 
 Routes:
-  GET /<slug>/          — full page with first page of entries
-  GET /<slug>/entries   — HTMX fragment for infinite scroll
+  GET  /<slug>/              — full page with first page of entries
+  GET  /<slug>/entries       — HTMX fragment for infinite scroll
+  POST /<slug>/tickets/adjust — adjust ticket quantity, returns HX-Refresh
 """
 from __future__ import annotations
 
@@ -78,4 +79,25 @@ def register() -> Blueprint:
         )
         return await make_response(html, 200)
 
+    @bp.post("/tickets/adjust")
+    async def adjust_ticket():
+        """Adjust ticket quantity and refresh the page."""
+        ident = current_cart_identity()
+        form = await request.form
+        entry_id = int(form.get("entry_id", 0))
+        count = max(int(form.get("count", 0)), 0)
+        tt_raw = (form.get("ticket_type_id") or "").strip()
+        ticket_type_id = int(tt_raw) if tt_raw else None
+
+        await services.calendar.adjust_ticket_quantity(
+            g.s, entry_id, count,
+            user_id=ident["user_id"],
+            session_id=ident["session_id"],
+            ticket_type_id=ticket_type_id,
+        )
+
+        resp = await make_response("", 200)
+        resp.headers["HX-Refresh"] = "true"
+        return resp
+
     return bp