fix: align FilePond upload with the Node.js API and proxy gallery previews

Use the filepond-image field, parse the API envelope, and load private files through the authenticated content endpoint so uploads persist and images display.

src/api/axiosInstance.js

@@ -29,6 +29,19 @@ axiosInstance.interceptors.request.use(
       config.params.lang = lang;
     }
 
+    const isFormData = typeof FormData !== 'undefined' && config.data instanceof FormData;
+    if (isFormData) {
+      // Let the browser set multipart boundary — a bare multipart/form-data header breaks Multer
+      if (typeof config.headers?.delete === 'function') {
+        config.headers.delete('Content-Type');
+        config.headers.delete('content-type');
+      } else {
+        delete config.headers['Content-Type'];
+        delete config.headers['content-type'];
+      }
+      config.timeout = Math.max(config.timeout || 0, 120000);
+    }
+
     return config;
   },
   (error) => Promise.reject(error)