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/filesApi.js

@@ -0,0 +1,15 @@
+// /src/api/filesApi.js
+import axiosInstance from './axiosInstance';
+
+export const filesApi = {
+  uploadTemp: (formData) => axiosInstance.post('/files/admin/upload-temp', formData, {
+    timeout: 120000
+  }),
+  getSignedUrl: (filename, bucket = 'temp') =>
+    axiosInstance.get(`/files/admin/signed-url/${encodeURIComponent(filename)}`, { params: { bucket } }),
+  getContent: (key, bucket) => axiosInstance.get('/files/admin/content', {
+    params: { key, bucket },
+    responseType: 'blob',
+    timeout: 120000
+  })
+};