fix: add 'website' to bookings source check constraint

Widget bookings use source='website' which violated the existing
constraint. Migration 069 expands the constraint to include 'website'.

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

backend/migrations/069_bookings_source_website.sql

@@ -0,0 +1,6 @@
+-- Migration 069 — Add 'website' to allowed booking sources
+
+ALTER TABLE bookings DROP CONSTRAINT IF EXISTS bookings_source_check;
+
+ALTER TABLE bookings ADD CONSTRAINT bookings_source_check
+  CHECK (source IN ('direct','booking_com','airbnb','expedia','vrbo','website','other'));