fix: tag color bug, FormData interceptor, falsy id check

- Fix tag using category_color instead of its own color when editing
- Add FormData auto-detection interceptor in client.ts (root cause of 422)
- Remove redundant Content-Type overrides from all 5 upload endpoints
- Fix falsy id check (id: 0 treated as null) with strict comparison
- Await invalidateQueries to prevent stale dropdown data

src/api/news.ts

@@ -66,10 +66,7 @@ export const newsApi = {
     const response = await apiClient.post<NewsMediaUploadResponse>(
       '/cabinet/admin/news/media/upload',
       formData,
-      {
-        headers: { 'Content-Type': 'multipart/form-data' },
-        signal,
-      },
+      { signal },
     );
     return response.data;
   },