chore: add SvelteKit nginx config, clean up Flask upstream, wire AE_APP_REPLICAS

- Add conf/nginx/site-enabled_aether_app_svelte_node.conf (SvelteKit node upstream)
- Clean up site-enabled_aether_flask_gunicorn.conf: remove dead comments, update
  upstream to app-node:3000
- docker-compose.yml: ae_app scale now uses ${AE_APP_REPLICAS:-1} instead of hardcoded 1

docker-compose.yml

@@ -143,7 +143,7 @@ services:
             target: deploy-node
             args:
                 BUILD_MODE: ${AE_APP_BUILD_MODE:-staging}
-        scale: 1
+        scale: ${AE_APP_REPLICAS:-1}
         env_file:
             - ./.env
         ports:
@@ -159,7 +159,7 @@ services:
             static.oneskyit.com: "104.237.143.4"
             dev.oneskyit.com: "192.168.32.7"
         # volumes:
-        #    # In production, the build happens INSIDE the container. 
+        #    # In production, the build happens INSIDE the container.
         #    # Mounting the host source here would override the internal build.
         #    # - ${AE_APP_SRC}:/app
         depends_on: