feat(frontend): add React chat UI with SSE parsing and source accordion

frontend/vite.config.ts

@@ -0,0 +1,20 @@
+import { defineConfig } from "vite";
+import react from "@vitejs/plugin-react";
+
+export default defineConfig({
+  plugins: [react()],
+  server: {
+    port: 5173,
+    proxy: {
+      "/api": {
+        target: "http://localhost:8000",
+        changeOrigin: true,
+      },
+    },
+  },
+  test: {
+    globals: true,
+    environment: "jsdom",
+    setupFiles: ["./src/test-setup.ts"],
+  },
+});