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/components/Header.tsx

@@ -133,7 +133,7 @@ export default function Header() {
           className="group flex items-center gap-3 min-w-0 desktop:shrink-0"
           onClick={() => setOpen(false)}
         >
-          <div className="relative flex items-center justify-center w-9 h-9 sm:w-10 sm:h-10 rounded-xl overflow-hidden shadow-sm ring-1 ring-ink/10 group-hover:ring-cobalt/40 group-hover:shadow-md group-hover:scale-105 transition-all duration-300 shrink-0">
+          <div className="relative flex items-center justify-center w-9 h-9 sm:w-10 sm:h-10 rounded-xl overflow-hidden shadow-sm border border-line group-hover:border-cobalt/40 group-hover:shadow-md group-hover:scale-105 transition-all duration-300 shrink-0">
             <svg viewBox="0 0 32 32" className="w-full h-full" aria-hidden="true">
               <defs>
                 <linearGradient id="headerLogoGrad" x1="0%" y1="0%" x2="100%" y2="100%">