ci(deploy): build+deploy frontend package (SSR standalone server)

Sebelumnya frontend hanya static export yang di-serve nginx di dalam package
proxy. Sekarang frontend = runtime mandiri (Next.js standalone :4017) yang
nginx proxikan ('/' -> Next server, '/api' + '/ws' -> backend :4001). Tambah
'frontend' ke matrix deploy agar dideploy + memulai unit gmw-frontend.

.github/workflows/deploy.yml

@@ -67,7 +67,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        service: [backend, discord-gateway, proxy]
+        service: [backend, discord-gateway, proxy, frontend]
     steps:
       - name: Checkout
         uses: actions/checkout@v7