feat: initial runner dashboard

Node 20 / no-framework HTTP service.
Routes: /healthz (no auth), /api/runners (proxy to GitHub), / (dashboard UI).
Dark theme, Basic Auth, 15s poll, stale-data strip, token-missing empty state.

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

Dockerfile

@@ -0,0 +1,10 @@
+FROM node:20-alpine
+
+WORKDIR /app
+
+COPY server.js .
+COPY index.html .
+
+EXPOSE 3000
+
+CMD ["node", "server.js"]