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

apps/aether-gateway/src/main.rs

@@ -495,7 +495,7 @@ impl GatewayLoggingArgs {
     about = "Phase 3a Rust ingress gateway for Aether"
 )]
 struct Args {
-    #[arg(long, env = "AETHER_GATEWAY_BIND", default_value = "0.0.0.0:80")]
+    #[arg(long, env = "AETHER_GATEWAY_BIND", default_value = "0.0.0.0:8084")]
     bind: String,
 
     /// 容器内健康检查入口：根据当前 bind 端口探测本地 /health。