refactor: 移除 Python upstream 依赖，清理全部 legacy/Python 兼容层

- 移除 upstream_base_url 参数及 AETHER_GATEWAY_UPSTREAM 环境变量，gateway 不再需要指向 Python 宿主
- 删除所有 LEGACY_*/PYTHON_* 常量、路由组、header 定义及 sunset/phaseout 机制
- 将 legacy_gateway_bridge 重命名为 internal_gateway，executor 相关命名统一为 execution_runtime
- dev.sh 新增 Postgres/Redis 预检查，移除 upstream 相关启动参数和提示
- 新增 ai_public 路由处理器
- 全量适配 handler、test、state、control 等模块的命名和接口变更

apps/aether-gateway/src/tunnel/embedded/hub.rs

@@ -832,7 +832,14 @@ impl HubStats {
 mod tests {
     use aether_runtime::bounded_queue;
 
-    use super::*;
+    use super::{
+        protocol, ControlPlaneClient, HubRouter, ProxyConn, MAX_REQUEST_BODY_FRAME_SIZE,
+    };
+    use axum::extract::ws::Message;
+    use bytes::Bytes;
+    use std::collections::HashMap;
+    use std::sync::Arc;
+    use tokio::sync::watch;
 
     fn build_meta() -> protocol::RequestMeta {
         protocol::RequestMeta {

apps/aether-gateway/src/tunnel/embedded/local_relay.rs

@@ -338,9 +338,11 @@ fn tunnel_error_response(status: StatusCode, kind: &str, message: &str) -> Respo
 #[cfg(test)]
 mod tests {
     use super::super::{AppState, ConnConfig, ControlPlaneClient};
-    use super::*;
+    use super::{relay_request, Body, Request, SocketAddr, StatusCode, TUNNEL_ERROR_HEADER};
+    use aether_contracts::tunnel::TUNNEL_RELAY_FORWARDED_BY_HEADER;
     use axum::extract::{ConnectInfo, Path, State};
     use axum::response::IntoResponse;
+    use std::time::Duration;
 
     fn test_app_state() -> AppState {
         AppState::new(

apps/aether-gateway/src/tunnel/mod.rs

@@ -799,10 +799,16 @@ fn parse_embedded_tunnel_heartbeat_request(
 
 #[cfg(test)]
 mod tests {
-    use super::*;
-    use aether_data::repository::proxy_nodes::{
-        InMemoryProxyNodeRepository, ProxyNodeReadRepository,
+    use super::{
+        apply_embedded_tunnel_heartbeat, apply_embedded_tunnel_node_status, current_unix_secs,
+        tunnel_attachment_key, TunnelAttachmentDirectory, TunnelAttachmentRecord,
+        GatewayDataState,
     };
+    use aether_data::repository::proxy_nodes::{
+        InMemoryProxyNodeRepository, ProxyNodeReadRepository, StoredProxyNode,
+    };
+    use serde_json::json;
+    use std::sync::Arc;
 
     fn sample_proxy_node(node_id: &str) -> StoredProxyNode {
         StoredProxyNode::new(