Add admin-core frontend (Port 3008)

Next.js admin frontend for Core with 3 categories
(Communication, Infrastructure, Development), 13 modules,
2 roles (developer, ops), and 11 API proxy routes.
Includes docker-compose service and nginx SSL config.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

admin-core/postcss.config.mjs

@@ -0,0 +1,9 @@
+/** @type {import('postcss-load-config').Config} */
+const config = {
+  plugins: {
+    tailwindcss: {},
+    autoprefixer: {},
+  },
+}
+
+export default config