feat: Extract Developer Portal as standalone Next.js app on port 3006

SDK customers can now access the documentation publicly without login.
The portal runs independently from admin-v2 on https://macmini:3006/.

- New developer-portal/ app with 26 pages, 2 components
- Docker service + nginx SSL reverse proxy on port 3006
- All /developers/* routes remapped to /* in the new app
- admin-v2 developer pages remain unchanged

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

developer-portal/tailwind.config.ts

@@ -0,0 +1,18 @@
+import type { Config } from 'tailwindcss'
+
+const config: Config = {
+  content: [
+    './components/**/*.{js,ts,jsx,tsx,mdx}',
+    './app/**/*.{js,ts,jsx,tsx,mdx}',
+  ],
+  theme: {
+    extend: {
+      fontFamily: {
+        sans: ['Inter', 'system-ui', 'sans-serif'],
+      },
+    },
+  },
+  plugins: [],
+}
+
+export default config