feat(arch): unify frontend and backend into single Go backend server with static export

- Configure Next.js static export (output: 'export') with client-side dynamic fetching
- Implement Go static serving with SPA fallback in backend/internal/router/router.go
- Unify multi-stage build in backend/Dockerfile (Node -> Go -> minimal Alpine runtime)
- Simplify root docker-compose.yml to single anl-app service on port 8080
- Update REQUIREMENTS.md DM-03 and AC-17 normative contracts to v3.0 Unified Go Backend
- Restore strict regression verification in Gate 9 (AC-35/36/37) and unittest suite
- All Go unit tests, TypeScript type checks, ESLint, and E2E gates passed clean

refer_landing_page/next.config.js

@@ -1,16 +1,8 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {
-  output: "standalone",
+  output: "export",
+  trailingSlash: true,
   reactStrictMode: true,
-  async redirects() {
-    return [
-      {
-        source: "/intro",
-        destination: "/",
-        permanent: true, // 308 permanent redirect (H-11 / IA-02)
-      },
-    ];
-  },
 };
 
 module.exports = nextConfig;