feat(azure): apply Azure SWA best practices for Next.js

- Add standalone output mode in next.config.mjs
- Configure environment variables with .env.example
- Update staticwebapp.config.json with proper routing and fallback
- Optimize GitHub Actions workflow with npm cache and env vars
- Set output_location to .next/standalone for SWA deployment
- Preserve all business logic in API client, auth, and components

next.config.mjs

@@ -1,11 +1,23 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {
+  // Azure SWA 最佳实践：输出独立服务器模式
+  output: 'standalone',
+  
   typescript: {
     ignoreBuildErrors: true,
   },
+  
   images: {
     unoptimized: true,
   },
+  
+  // 环境变量配置
+  env: {
+    NEXT_PUBLIC_DATA_INGESTION_URL: process.env.NEXT_PUBLIC_DATA_INGESTION_URL,
+    NEXT_PUBLIC_MCP_SERVER_URL: process.env.NEXT_PUBLIC_MCP_SERVER_URL,
+    NEXT_PUBLIC_API_GATEWAY_URL: process.env.NEXT_PUBLIC_API_GATEWAY_URL,
+  },
+  
   async redirects() {
     return [
       {