feat: initialize cart app with blueprints, templates, and CI

Extract cart, order, and orders blueprints with their service layer,
templates, Dockerfile (APP_MODULE=app:app, IMAGE=cart), entrypoint,
and Gitea CI workflow from the coop monolith.

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

bp/cart/services/check_sumup_status.py

@@ -0,0 +1,35 @@
+from suma_browser.app.payments.sumup import get_checkout as sumup_get_checkout
+from sqlalchemy import update
+from models.calendars import CalendarEntry  # NEW
+
+
+async def check_sumup_status(session, order):
+    checkout_data = await sumup_get_checkout(order.sumup_checkout_id)
+    order.sumup_status = checkout_data.get("status") or order.sumup_status
+    sumup_status = (order.sumup_status or "").upper()
+
+    if sumup_status == "PAID":
+        if order.status != "paid":
+            order.status = "paid"
+            filters = [
+                CalendarEntry.deleted_at.is_(None),
+                CalendarEntry.state == "ordered",
+                CalendarEntry.order_id==order.id,
+            ]
+            if order.user_id is not None:
+                filters.append(CalendarEntry.user_id == order.user_id)
+            elif order.session_id is not None:
+                filters.append(CalendarEntry.session_id == order.session_id)
+
+            await session.execute(
+                update(CalendarEntry)
+                .where(*filters)
+                .values(state="provisional")
+            )
+            # also clear cart for this user/session if it wasn't already
+    elif sumup_status == "FAILED":
+        order.status = "failed"
+    else:
+        order.status = sumup_status.lower() or order.status
+
+    await g.s.flush()