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/audit/shadow.rs

@@ -154,7 +154,7 @@ mod tests {
     #[tokio::test]
     async fn records_shadow_result_for_ai_public_response() {
         let repository = Arc::new(InMemoryShadowResultRepository::default());
-        let state = AppState::new("http://127.0.0.1:18084")
+        let state = AppState::new()
             .expect("app state should build")
             .with_shadow_result_data_writer_for_tests(repository.clone());
         let response = Response::builder()
@@ -205,7 +205,7 @@ mod tests {
     #[tokio::test]
     async fn merges_rust_and_python_shadow_samples_into_match() {
         let repository = Arc::new(InMemoryShadowResultRepository::default());
-        let state = AppState::new("http://127.0.0.1:18084")
+        let state = AppState::new()
             .expect("app state should build")
             .with_shadow_result_data_repository_for_tests(repository.clone());
         let response = Response::builder()