refactor: 移除独立 hub/proxy/executor/gateway crate，统一为 gateway tunnel 架构

- 删除 aether-hub、aether-proxy 独立项目及其 Dockerfile/配置
- 删除 crates/aether-executor 和 crates/aether-gateway 全部模块
- 新增 apps/ 目录作为应用入口
- 将 hub 概念重构为 gateway tunnel transport
- 将 executor 重构为 execution runtime
- 新增 tunnel.rs 合约定义和 testkit tunnel/execution_runtime 模块
- 更新 Python 服务层和测试适配新架构命名

apps/aether-gateway/Cargo.toml

@@ -0,0 +1,48 @@
+[package]
+name = "aether-gateway"
+version = "0.1.0"
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+description = "Rust ingress gateway for Aether phase 3a transparent proxy"
+
+[dependencies]
+aether-billing.workspace = true
+aether-cache.workspace = true
+aether-contracts.workspace = true
+aether-crypto.workspace = true
+aether-data.workspace = true
+aether-http.workspace = true
+aether-runtime.workspace = true
+aether-wallet.workspace = true
+async-stream.workspace = true
+async-trait.workspace = true
+axum = { version = "0.8", features = ["ws"] }
+base64.workspace = true
+bcrypt.workspace = true
+bytes.workspace = true
+chrono.workspace = true
+chrono-tz.workspace = true
+clap = { version = "4", features = ["derive", "env"] }
+dashmap = "6"
+flate2.workspace = true
+futures-util.workspace = true
+hmac.workspace = true
+http.workspace = true
+ldap3 = "0.11"
+parking_lot = "0.12"
+regex.workspace = true
+redis.workspace = true
+reqwest.workspace = true
+rustls.workspace = true
+serde.workspace = true
+serde_json.workspace = true
+sha2.workspace = true
+sqlx.workspace = true
+thiserror.workspace = true
+tokio.workspace = true
+tokio-util.workspace = true
+tracing.workspace = true
+url.workspace = true
+uuid.workspace = true
+webpki-roots.workspace = true