Phase 5: Replace cross-domain writes with glue services, emit events

- checkout.py: use claim_entries_for_order(), emit order.created
- check_sumup_status.py: use confirm_entries_for_order(), emit order.paid
- global_routes.py: use get_entries_for_order() instead of relationship
- order.py: remove calendar_entries relationship
- api.py: remove /adopt endpoint (replaced by event-driven adoption)

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

models/order.py

@@ -69,11 +69,6 @@ class Order(Base):
         cascade="all, delete-orphan",
         lazy="selectin",
     )
-    calendar_entries: Mapped[List["CalendarEntry"]] = relationship(
-        "CalendarEntry",
-        back_populates="order",
-        lazy="selectin",
-    )
     page_config: Mapped[Optional["PageConfig"]] = relationship(
         "PageConfig",
         foreign_keys=[page_config_id],