feat(backend): integrate custom services across booking, payment, scheduling, today, and user modules

Update booking create/confirm/progress/reserve handlers to support custom_service_ids and custom overrides. Add UNION ALL queries to include custom_services in booking detail, payment summary, scheduling availability, today dashboard, and customer relationship queries.

Ultraworked with Sisyphus (https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/handlers/user/customer_relationship.go

@@ -135,12 +135,21 @@ func GetCustomerRelationshipHandler(w http.ResponseWriter, r *http.Request) {
 	}
 
 	rows, err := db.DB.Query(r.Context(), `
-		SELECT s.name, COUNT(*) as count
-		FROM booking_services bsvc
-		JOIN bookings b ON bsvc.booking_id = b.id
-		JOIN services s ON bsvc.service_id = s.id
-		WHERE b.user_id = $1 AND b.status = 'completed'
-		GROUP BY s.name
+		SELECT name, cnt FROM (
+			SELECT s.name, COUNT(*) as count, COUNT(*) as cnt
+			FROM booking_services bsvc
+			JOIN bookings b ON bsvc.booking_id = b.id
+			JOIN services s ON bsvc.service_id = s.id
+			WHERE b.user_id = $1 AND b.status = 'completed'
+			GROUP BY s.name
+			UNION ALL
+			SELECT cs.name, COUNT(*) as count, COUNT(*) as cnt
+			FROM booking_custom_services bcs
+			JOIN bookings b ON bcs.booking_id = b.id
+			JOIN custom_services cs ON bcs.custom_service_id = cs.id
+			WHERE b.user_id = $1 AND b.status = 'completed'
+			GROUP BY cs.name
+		) combined
 		ORDER BY count DESC
 		LIMIT 5
 	`, userID)