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/scheduling/default-hours.go

@@ -408,18 +408,23 @@ func GetAvailableHours(w http.ResponseWriter, r *http.Request) {
 	bookingRows, _ := db.DB.Query(r.Context(), `
 		SELECT
 			b.start_time,
-			COALESCE(SUM(
-				CASE
+			COALESCE((SELECT SUM(dur) FROM (
+				SELECT CASE
 					WHEN bs.override_duration_minutes IS NOT NULL AND bs.override_duration_minutes > 0
 						THEN bs.override_duration_minutes
 					ELSE s.duration_minutes
+				END AS dur
+				FROM booking_services bs LEFT JOIN services s ON bs.service_id = s.id WHERE bs.booking_id = b.id
+				UNION ALL
+				SELECT CASE
+					WHEN bcs.override_duration_minutes IS NOT NULL AND bcs.override_duration_minutes > 0
+						THEN bcs.override_duration_minutes
+					ELSE cs.duration_minutes
 				END
-			), 0) AS total_duration
+				FROM booking_custom_services bcs LEFT JOIN custom_services cs ON bcs.custom_service_id = cs.id WHERE bcs.booking_id = b.id
+			) sub), 0) AS total_duration
 		FROM bookings b
-		LEFT JOIN booking_services bs ON b.id = bs.booking_id
-		LEFT JOIN services s ON bs.service_id = s.id
 		WHERE b.start_time >= $1 AND b.start_time <= $2
-		GROUP BY b.id, b.start_time
 		ORDER BY b.start_time
 	`, start, end)