fix: add qr to reviews source constraint + notif type fix

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

backend/migrations/090_reviews_source_qr.sql

@@ -0,0 +1,7 @@
+-- Migration 090 — Add 'qr' to reviews source constraint
+
+ALTER TABLE reviews DROP CONSTRAINT IF EXISTS reviews_source_check;
+
+ALTER TABLE reviews
+  ADD CONSTRAINT reviews_source_check
+  CHECK (source IN ('direct', 'booking_com', 'airbnb', 'google', 'tripadvisor', 'qr'));