fix: add HEALTHCHECK to Dockerfile for Coolify health gate

Coolify inspects Docker .State.Health.Status; container needs a
HEALTHCHECK instruction for the health gate to pass.

Agent-Session: runner-dashboard-deploy-2026-06-19

Dockerfile

@@ -1,5 +1,7 @@
 FROM node:20-alpine
 
+RUN apk add --no-cache wget
+
 WORKDIR /app
 
 COPY server.js .
@@ -7,4 +9,7 @@ COPY index.html .
 
 EXPOSE 3000
 
+HEALTHCHECK --interval=30s --timeout=5s --start-period=20s --retries=3 \
+  CMD wget -qO- http://localhost:3000/healthz || exit 1
+
 CMD ["node", "server.js"]