Ship dashboard build config

Proof: Include the Vite config required for the dashboard-builder image stage to build operator-dashboard static assets during deployment.

Assumptions: The current Vite config in the worktree is the intended build config for the deployed operator-dashboard frontend.

Still fake: External alert receiver remains unconfigured; this commit only resolves the image-build blocker for the dashboard deploy.

vite.operator-dashboard.config.mjs

@@ -0,0 +1,41 @@
+import react from '@vitejs/plugin-react';
+import { defineConfig } from 'vite';
+
+function buildProxyConfig({ target, authHeader, websocket = false }) {
+  return {
+    target,
+    changeOrigin: true,
+    ws: websocket,
+    configure(proxy) {
+      if (!authHeader) return;
+      proxy.on('proxyReq', (proxyReq) => {
+        proxyReq.setHeader('Authorization', authHeader);
+      });
+      proxy.on('proxyReqWs', (proxyReq) => {
+        proxyReq.setHeader('Authorization', authHeader);
+      });
+    },
+  };
+}
+
+const target = process.env.OPERATOR_DASHBOARD_DEV_UPSTREAM_URL || 'http://127.0.0.1:18090';
+const authHeader = process.env.OPERATOR_DASHBOARD_DEV_BASIC_AUTH_HEADER || '';
+
+export default defineConfig({
+  plugins: [react()],
+  root: 'src/operator-dashboard/static',
+  build: {
+    outDir: '../dist',
+    emptyOutDir: true,
+  },
+  server: {
+    host: process.env.OPERATOR_DASHBOARD_DEV_HOST || '127.0.0.1',
+    port: Number(process.env.OPERATOR_DASHBOARD_DEV_PORT || 5173),
+    strictPort: true,
+    proxy: {
+      '/api': buildProxyConfig({ target, authHeader }),
+      '/healthz': buildProxyConfig({ target, authHeader }),
+      '/ws': buildProxyConfig({ target, authHeader, websocket: true }),
+    },
+  },
+});