refactor: comment out placement endpoint in AdController for future removal

apps/box-app-api/src/feature/ads/ad.controller.ts

@@ -21,6 +21,8 @@ export class AdController {
    *
    * Returns a single AdDto or null (if no suitable ad is found).
    * Your global response interceptor will wrap this into the standard envelope.
+   *
+   * remove this placement endpoint for now
    */
   // @Get('placement')
   // @ApiOperation({