feat(tunnel): 引入 aether-hub 帧路由器，支持多 worker 共享 tunnel 连接

新增 Rust 实现的 aether-hub 服务，作为 Docker 容器内部 WebSocket 帧路由器，
解决多 Gunicorn worker 进程间 tunnel 连接隔离问题。

主要改动：
- 新增 aether-hub Rust 项目，实现 proxy/worker 双向帧路由与 stream_id 重映射
- 新增 HubConnectionManager/HubTunnelTransport，worker 通过 Hub 转发 tunnel 帧
- 新增 create_tunnel_transport 工厂函数，按运行环境自动选择 Hub 或直连模式
- 新增 NODE_STATUS 广播机制，Hub 实时通知所有 worker 节点连接状态变化
- CI/CD 新增 build-hub job，Dockerfile 集成 Hub 二进制，deploy.sh 适配 Hub 构建
- 默认 GUNICORN_WORKERS 从 4 降为 2

aether-hub/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "aether-hub"
+version = "0.1.0"
+edition = "2021"
+description = "Tunnel Hub for Aether - frame router between workers and proxies"
+
+[dependencies]
+tokio = { version = "1", features = ["full"] }
+axum = { version = "0.8", features = ["ws"] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+clap = { version = "4", features = ["derive", "env"] }
+dashmap = "6"
+parking_lot = "0.12"
+flate2 = "1"
+futures-util = "0.3"
+
+[profile.release]
+lto = true
+strip = true
+codegen-units = 1