feat: add gated housekeeping foundation preview

.env.example

@@ -17,6 +17,8 @@ NODE_ENV=production
 PORT=3002
 NEXT_TELEMETRY_DISABLED=1
 UV_THREADPOOL_SIZE=16
+# Non-production preview only; production always returns 404.
+HOUSEKEEPING_NEXT_PREVIEW_ENABLED=false
 
 # --- HOTEL & URLS ---
 HOTEL_NAME=EPIC WEB CONTROL