fix: Add SETGID/SETUID capabilities to backend service in production profile

The purple-mcp-streamable-http service needs these capabilities to run
Python with user/group switching. This fixes the 502 Bad Gateway error
when nginx tries to proxy to the backend service.

Author: michaelmoore-s1

docker-compose.yml

@@ -59,6 +59,9 @@ services:
       - no-new-privileges:true
     cap_drop:
       - ALL
+    cap_add:
+      - SETGID  # Python and child processes need to setgid
+      - SETUID  # Python and child processes need to setuid
     healthcheck:
       test: ["CMD", "wget", "--spider", "-q", "http://localhost:8000/health"]
       interval: 30s