FIX: Allow axios to auto-detect Content-Type for FormData uploads

frontend/lib/api.ts

@@ -2,15 +2,16 @@ import axios from 'axios';
 
 const api = axios.create({
   baseURL: process.env.NEXT_PUBLIC_API_URL || '/api/v1',
-  headers: {
-    'Content-Type': 'application/json',
-  },
   withCredentials: true, // Send cookies with requests
 });
 
-// Request interceptor - cookies are sent automatically with withCredentials
+// Request interceptor - set Content-Type based on data type
 api.interceptors.request.use((config) => {
-  // Token is sent via cookie, no need to add Authorization header
+  // Let axios auto-detect Content-Type for FormData
+  // Only set application/json for non-FormData requests
+  if (!(config.data instanceof FormData)) {
+    config.headers['Content-Type'] = 'application/json';
+  }
   return config;
 });