feat(notifications): add admin notification acknowledgement on booking state changes

- Add AcknowledgePendingBookingNotification helper for acknowledging notifications
- ConfirmBookingHandler: acknowledge pending notification when booking confirmed
- Cancel handlers: acknowledge pending notification and only create cancelled_booking notification if booking was not in pending status
- Add user_notification_preferences table with email, sms, push enabled flags
- Update cancellation logic to check original status before creating notifications

backend/handlers/notifications/notifications.go

@@ -1,6 +1,7 @@
 package notifications
 
 import (
+	"context"
 	"crussell/db"
 	"database/sql"
 	"encoding/json"
@@ -11,6 +12,7 @@ import (
 	"time"
 
 	"github.com/go-chi/chi/v5"
+	"github.com/jackc/pgx/v5/pgconn"
 )
 
 // Structs returned in JSON
@@ -173,3 +175,19 @@ func AcknowledgeNotification(w http.ResponseWriter, r *http.Request) {
 		"status": "ok",
 	})
 }
+
+func AcknowledgePendingBookingNotification(tx interface{}, ctx context.Context, bookingID string) error {
+	query := `
+		UPDATE admin_notifications 
+		SET acknowledged_at = NOW() 
+		WHERE booking_id = $1 AND reason = 'pending_booking' AND acknowledged_at IS NULL
+	`
+	_, err := tx.(interface {
+		Exec(ctx context.Context, sql string, arguments ...interface{}) (pgconn.CommandTag, error)
+	}).Exec(ctx, query, bookingID)
+	if err != nil {
+		log.Printf("Failed to acknowledge pending booking notification for %s: %v", bookingID, err)
+		return err
+	}
+	return nil
+}