Add internal authentication configuration and middleware support

- Enable internal authentication via environment variable in .env.example
- Update nuxt.config.ts to include internalAuthEnabled check
- Modify internal-auth middleware to conditionally enforce authentication based on the new configuration

server/middleware/internal-auth.ts

@@ -13,13 +13,20 @@ export default defineEventHandler((event) => {
 
   const config = useRuntimeConfig()
 
+  // Skip auth if internal auth is not enabled
+  if (!config.internalAuthEnabled) {
+    return
+  }
+
   // Get credentials from environment variables
   const validUsername = config.internalAuthUsername
   const validPassword = config.internalAuthPassword
 
   // Skip auth if credentials are not configured (development convenience)
   if (!validUsername || !validPassword) {
-    console.warn('⚠️  INTERNAL_AUTH_USERNAME or INTERNAL_AUTH_PASSWORD not set. /internal routes are unprotected!')
+    console.warn(
+      '⚠️  INTERNAL_AUTH_USERNAME or INTERNAL_AUTH_PASSWORD not set. /internal routes are unprotected!'
+    )
     return
   }