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/lib/adminApi.ts

@@ -5,14 +5,10 @@
 
 export function getAdminApiBaseUrl(): string {
   if (typeof window !== "undefined") {
-    // Browser / CSR context: use public endpoint
-    return (
-      process.env.NEXT_PUBLIC_API_BASE_URL ||
-      process.env.API_BASE_URL ||
-      "http://localhost:8080/api/v1"
-    );
+    // Browser / CSR context: same-origin relative path by default.
+    return process.env.NEXT_PUBLIC_API_BASE_URL || "/api/v1";
   }
-  // Server / SSR context: prefer internal container DNS if available, fallback to NEXT_PUBLIC or localhost
+  // Server / build-time context: defensive fallback during static prerendering
   return (
     process.env.API_BASE_URL ||
     process.env.NEXT_PUBLIC_API_BASE_URL ||

refer_landing_page/lib/api.ts

@@ -12,14 +12,10 @@ import type {
 
 export function getApiBaseUrl(): string {
   if (typeof window !== "undefined") {
-    // Browser / CSR context: use public endpoint
-    return (
-      process.env.NEXT_PUBLIC_API_BASE_URL ||
-      process.env.API_BASE_URL ||
-      "http://localhost:8080/api/v1"
-    );
+    // Browser / CSR context: same-origin relative path by default.
+    return process.env.NEXT_PUBLIC_API_BASE_URL || "/api/v1";
   }
-  // Server / SSR context: prefer internal container DNS if available, fallback to NEXT_PUBLIC or localhost
+  // Server / build-time context: defensive fallback during static prerendering
   return (
     process.env.API_BASE_URL ||
     process.env.NEXT_PUBLIC_API_BASE_URL ||