Phase 5: Drop cross-domain FK constraints (events → cart)

Merge three alembic heads and drop:
- calendar_entries.order_id FK → orders.id
- tickets.order_id FK → orders.id

Columns kept as plain integers for glue-service bridging.

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

alembic/versions/j0h8e4f6g7_drop_cross_domain_fks.py

@@ -0,0 +1,51 @@
+"""drop cross-domain FK constraints (events → cart)
+
+Merge three existing heads and remove:
+- calendar_entries.order_id FK → orders.id
+- tickets.order_id FK → orders.id
+
+Columns are kept as plain integers.
+
+Revision ID: j0h8e4f6g7
+Revises: c3d4e5f6a7b8, i9g7d3e5f6, g7e5b1c3d4f8
+Create Date: 2026-02-14
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = 'j0h8e4f6g7'
+down_revision = ('c3d4e5f6a7b8', 'i9g7d3e5f6', 'g7e5b1c3d4f8')
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.drop_constraint(
+        'fk_calendar_entries_order_id',
+        'calendar_entries',
+        type_='foreignkey',
+    )
+    op.drop_constraint(
+        'tickets_order_id_fkey',
+        'tickets',
+        type_='foreignkey',
+    )
+
+
+def downgrade() -> None:
+    op.create_foreign_key(
+        'fk_calendar_entries_order_id',
+        'calendar_entries',
+        'orders',
+        ['order_id'],
+        ['id'],
+        ondelete='SET NULL',
+    )
+    op.create_foreign_key(
+        'tickets_order_id_fkey',
+        'tickets',
+        'orders',
+        ['order_id'],
+        ['id'],
+        ondelete='SET NULL',
+    )