Issue #3590178: Fix mismatched Drupal.t() placeholder in max file size validation

The max_size() function in s3fs_cors.js uses %maxSizeMB in the format string but %maxSize in the replacement object. Since % placeholders in Drupal.t() wrap their value in <em class="placeholder">, the mismatch means the replacement never matches and raw HTML appears in the error message. Switches to @maxSize (plain text output) and adds Math.round() for a clean integer.