fix(containerd): add pid:host for CNI netns access and runtime deps to MCP image

- Add pid: host to containerd service so server can access MCP container
  network namespaces via /proc/PID/ns/net for CNI setup
- Add Node.js, npm, Python 3, uv to embedded MCP image rootfs so users
  can run npx/uvx MCP servers inside containers

docker-compose.yml

@@ -44,6 +44,7 @@ services:
       dockerfile: docker/Dockerfile.containerd
     container_name: memoh-containerd
     privileged: true
+    pid: host
     volumes:
       - containerd_sock:/run/containerd
       - containerd_data:/var/lib/containerd