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/nginx.conf

@@ -0,0 +1,18 @@
+server {
+    listen 80;
+    root /usr/share/nginx/html;
+    index index.html;
+
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+
+    location /api {
+        proxy_pass http://api:8000;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+    }
+
+    gzip on;
+    gzip_types text/plain text/css application/json application/javascript;
+}