fix(gateway): 默认监听端口改为 8084 以支持非 root 运行

- Dockerfile 及 main.rs 默认 bind 从 0.0.0.0:80 改为 0.0.0.0:8084
- docker-compose 以 UID:GID 非 root 用户启动 app 容器
- compose 端口映射与容器内监听端口保持一致，通过 AETHER_GATEWAY_BIND 注入

Dockerfile.app

@@ -19,10 +19,10 @@ COPY dist/frontend/ /srv/frontend
 WORKDIR /app
 
 ENV RUST_LOG=aether_gateway=info \
-    AETHER_GATEWAY_BIND=0.0.0.0:80 \
+    AETHER_GATEWAY_BIND=0.0.0.0:8084 \
     AETHER_GATEWAY_STATIC_DIR=/srv/frontend
 
-EXPOSE 80
+EXPOSE 8084
 
 HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
     CMD ["/usr/local/bin/aether-gateway", "--healthcheck"]