feat: add dashboard source code with Vite + React + Recharts and CI/CD build

- Reconstruct dashboard from compiled container: App.jsx, main.jsx, index.css
- nginx.conf with SPA routing and /api proxy to api:8000
- Multi-stage Dockerfile: node:20-alpine build + nginx:alpine serve
- Add third kaniko build step in ci.yml for chemavx/polymarket-bot-dashboard
- Update k8s manifest sed to patch deployment-dashboard.yaml image on each push

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

dashboard/src/main.jsx

@@ -0,0 +1,10 @@
+import React from 'react'
+import ReactDOM from 'react-dom/client'
+import App from './App.jsx'
+import './index.css'
+
+ReactDOM.createRoot(document.getElementById('root')).render(
+  <React.StrictMode>
+    <App />
+  </React.StrictMode>
+)