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/handlers/admin/provider_models/available_source.rs

@@ -0,0 +1,37 @@
+use super::*;
+
+pub(super) async fn maybe_handle(
+    state: &AppState,
+    request_context: &GatewayPublicRequestContext,
+    _request_body: Option<&axum::body::Bytes>,
+    decision: &GatewayControlDecision,
+) -> Result<Option<Response<Body>>, GatewayError> {
+    if decision.route_family.as_deref() == Some("provider_models_manage")
+        && decision.route_kind.as_deref() == Some("available_source_models")
+        && request_context.request_method == http::Method::GET
+    {
+        let Some(provider_id) =
+            admin_provider_available_source_models_path(&request_context.request_path)
+        else {
+            return Ok(Some(
+                (
+                    http::StatusCode::NOT_FOUND,
+                    Json(json!({ "detail": "Provider 不存在" })),
+                )
+                    .into_response(),
+            ));
+        };
+        return Ok(Some(
+            match build_admin_provider_available_source_models_payload(state, &provider_id).await {
+                Some(payload) => Json(payload).into_response(),
+                None => (
+                    http::StatusCode::NOT_FOUND,
+                    Json(json!({ "detail": format!("Provider {provider_id} 不存在") })),
+                )
+                    .into_response(),
+            },
+        ));
+    }
+
+    Ok(None)
+}