feat: add Matrix chat notification support (#211)

Implements native Matrix notification channel support, allowing users
to receive service alerts in any Matrix room via the Client-Server API.

Changes:
- server/service-operation/notification/matrix.go: new Matrix service
  implementing the NotificationService interface (PUT /_matrix/client/v3/...)
- server/service-operation/notification/types.go: add MatrixHomeserver,
  MatrixRoomID, MatrixAccessToken fields to AlertConfiguration
- server/service-operation/notification/manager.go: register MatrixService
- server/pb_migrations/1772200000_updated_alert_configurations_matrix.js:
  PocketBase migration adding matrix fields and notification_type value
- application: Matrix option in channel dialog with homeserver/room/token
  fields, tab filter, list display, type definitions and translations (en, km)
- application/public/upload/notification/matrix.png: Matrix channel icon

application/src/components/settings/notification-settings/NotificationChannelList.tsx

@@ -82,6 +82,7 @@ export const NotificationChannelList = ({
       case "pushover": return "Pushover";
       case "notifiarr": return "Notifiarr";
       case "webhook": return "Webhook";
+      case "matrix": return "Matrix";
       default: return type || "Unknown";
     }
   };
@@ -102,6 +103,8 @@ export const NotificationChannelList = ({
         return config.signal_number || '';
       case "email":
         return config.email_address || '';
+      case "matrix":
+        return config.matrix_room_id || '';
       default:
         return '';
     }