Add /auth/ location to nginx proxy config

The /auth/ path was not being proxied to Django, causing POST
requests to authentication endpoints to return 405 errors.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/nginx.conf

@@ -54,6 +54,15 @@ http {
             proxy_set_header X-Forwarded-Proto $scheme;
         }
 
+        # Proxy Auth requests to Django
+        location /auth/ {
+            proxy_pass http://django:5000;
+            proxy_set_header Host $host;
+            proxy_set_header X-Real-IP $remote_addr;
+            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+            proxy_set_header X-Forwarded-Proto $scheme;
+        }
+
         # Proxy Admin requests to Django
         location /admin/ {
             proxy_pass http://django:5000;