feat: implement Dockerfile and service scripts for yanpm-agent

apps/agent/docker/s6/services.d/agent/run

@@ -0,0 +1,4 @@
+#!/bin/sh
+# Run the agent as the unprivileged 'app' user
+cd /app
+exec s6-setuidgid app ./yanpm-agent

apps/agent/docker/s6/services.d/nginx/run

@@ -0,0 +1,3 @@
+#!/bin/sh
+# Run nginx in foreground (s6 will supervise it)
+exec nginx -g 'daemon off;'