Fix PDF download: Handle binary file responses in API proxy

frontend/src/app/api/[...path]/route.ts

@@ -71,14 +71,41 @@ async function proxyToBackend(request: NextRequest, pathSegments: string[]) {
 
     const response = await fetch(url, options);
     
-    // Get response body
+    // Check if this is a file download (binary response)
+    const contentType = response.headers.get('content-type') || '';
+    const isFileDownload = contentType.includes('application/pdf') || 
+                          contentType.includes('application/octet-stream') ||
+                          response.headers.get('content-disposition');
+    
+    // Handle binary file downloads differently
+    if (isFileDownload) {
+      const blob = await response.blob();
+      const headers = new Headers();
+      
+      // Copy important headers for file downloads
+      if (response.headers.get('content-type')) {
+        headers.set('Content-Type', response.headers.get('content-type')!);
+      }
+      if (response.headers.get('content-disposition')) {
+        headers.set('Content-Disposition', response.headers.get('content-disposition')!);
+      }
+      if (response.headers.get('content-length')) {
+        headers.set('Content-Length', response.headers.get('content-length')!);
+      }
+      
+      return new NextResponse(blob, {
+        status: response.status,
+        headers,
+      });
+    }
+    
+    // Handle regular JSON/text responses
     const data = await response.text();
     
-    // Return response with same status and headers
     return new NextResponse(data, {
       status: response.status,
       headers: {
-        'Content-Type': response.headers.get('content-type') || 'application/json',
+        'Content-Type': contentType || 'application/json',
       },
     });
   } catch (error) {