build(dev): proxy /api in dev and preview so the production bundle is testable

vite.config.ts

@@ -3,10 +3,34 @@ import react from '@vitejs/plugin-react'
 import tailwindcss from '@tailwindcss/vite'
 
 // https://vite.dev/config/
+/**
+ * The backend, for the two dev-time servers. Production does not use either of
+ * these — nginx or httpd proxies /api/ there — but `npm run preview` serves the
+ * real production bundle, which is built with a *relative* API base and so has
+ * no host to call without a proxy in front of it. Without this block the only
+ * way to exercise the shipped artifact is to deploy it, which is how a bundle
+ * reaches a demo server untested.
+ */
+const API_TARGET = 'http://127.0.0.1:8082'
+
+const proxy = {
+  '/api': {
+    target: API_TARGET,
+    changeOrigin: true,
+  },
+}
+
 export default defineConfig({
   plugins: [react(), tailwindcss()],
   server: {
     // 5180 belongs to BharatLinc-UI — UdyamLinc runs alongside it
     port: 5182,
+    proxy,
+  },
+  // Serves dist/ exactly as it will be served in production, with the same
+  // relative API base, so a preview run is a real rehearsal of the deployment.
+  preview: {
+    port: 4173,
+    proxy,
   },
 })