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/src/api/backend/admin.rs

@@ -0,0 +1,8 @@
+use axum::routing::any;
+use axum::Router;
+
+use crate::gateway::{proxy_request, AppState};
+
+pub(crate) fn mount_admin_routes(router: Router<AppState>) -> Router<AppState> {
+    router.route("/api/admin/{*admin_path}", any(proxy_request))
+}

apps/aether-gateway/src/api/backend/internal.rs

@@ -0,0 +1,19 @@
+use axum::routing::{any, get, post};
+use axum::Router;
+
+use crate::gateway::{
+    proxy_request, proxy_tunnel, relay_request, AppState, PROXY_TUNNEL_PATH, TUNNEL_HEARTBEAT_PATH,
+    TUNNEL_NODE_STATUS_PATH, TUNNEL_RELAY_PATH_PATTERN,
+};
+
+pub(crate) fn mount_internal_routes(router: Router<AppState>) -> Router<AppState> {
+    router
+        .route(
+            "/api/internal/gateway/{*legacy_gateway_path}",
+            any(proxy_request),
+        )
+        .route(PROXY_TUNNEL_PATH, get(proxy_tunnel))
+        .route(TUNNEL_HEARTBEAT_PATH, post(proxy_request))
+        .route(TUNNEL_NODE_STATUS_PATH, post(proxy_request))
+        .route(TUNNEL_RELAY_PATH_PATTERN, post(relay_request))
+}

apps/aether-gateway/src/api/backend/mod.rs

@@ -0,0 +1,9 @@
+mod admin;
+mod internal;
+mod oauth;
+mod public;
+
+pub(crate) use admin::mount_admin_routes;
+pub(crate) use internal::mount_internal_routes;
+pub(crate) use oauth::mount_oauth_routes;
+pub(crate) use public::mount_public_support_routes;

apps/aether-gateway/src/api/backend/oauth.rs

@@ -0,0 +1,13 @@
+use axum::routing::{any, get};
+use axum::Router;
+
+use crate::gateway::{proxy_request, AppState};
+
+pub(crate) fn mount_oauth_routes(router: Router<AppState>) -> Router<AppState> {
+    router
+        .route("/api/oauth/providers", get(proxy_request))
+        .route("/api/oauth/{*oauth_public_path}", get(proxy_request))
+        .route("/api/user/oauth/bindable-providers", get(proxy_request))
+        .route("/api/user/oauth/links", get(proxy_request))
+        .route("/api/user/oauth/{*oauth_user_path}", any(proxy_request))
+}

apps/aether-gateway/src/api/backend/public.rs

@@ -0,0 +1,28 @@
+use axum::routing::get;
+use axum::Router;
+
+use crate::gateway::{proxy_request, AppState};
+
+pub(crate) fn mount_public_support_routes(router: Router<AppState>) -> Router<AppState> {
+    router
+        .route("/v1/models", get(proxy_request))
+        .route("/v1beta/models", get(proxy_request))
+        .route("/v1/health", get(proxy_request))
+        .route("/health", get(proxy_request))
+        .route("/v1/providers", get(proxy_request))
+        .route("/v1/providers/{*provider_path}", get(proxy_request))
+        .route("/v1/test-connection", get(proxy_request))
+        .route("/test-connection", get(proxy_request))
+        .route("/api/public/site-info", get(proxy_request))
+        .route("/api/public/providers", get(proxy_request))
+        .route("/api/public/models", get(proxy_request))
+        .route("/api/public/search/models", get(proxy_request))
+        .route("/api/public/stats", get(proxy_request))
+        .route("/api/public/global-models", get(proxy_request))
+        .route("/api/public/health/api-formats", get(proxy_request))
+        .route("/api/modules/auth-status", get(proxy_request))
+        .route("/api/capabilities", get(proxy_request))
+        .route("/api/capabilities/user-configurable", get(proxy_request))
+        .route("/api/capabilities/model/{*model_path}", get(proxy_request))
+        .route("/", get(proxy_request))
+}