refactor: 移除 Python 后端源码，全面迁移至 Rust gateway 架构

- 删除全部 Python 源码 (src/) 及 Alembic 迁移脚本，归档至 _deprecated_py_src/
- 重构 Rust gateway ai_pipeline: 拆分 planner/finalize 模块，新增 contracts/adaptation 层
- 重组 handlers 模块为 admin/public/proxy/internal/shared 子模块结构
- 新增 executor 模块，引入 Rust 原生数据库迁移 (aether-data/migrations)
- 简化 CI/Docker 构建流程，移除 base image 二级构建，统一为单一 app image
- 移除 Python 相关基础设施文件 (entrypoint.sh, gunicorn_conf.py, Dockerfile.base)

apps/aether-gateway/src/execution_runtime/submission.rs

@@ -1,12 +1,13 @@
+use crate::gateway::ai_pipeline::adaptation::private_envelope::normalize_provider_private_response_value as unwrap_local_finalize_response_value;
 use crate::gateway::ai_pipeline::conversion::{
     build_core_error_body_for_client_format, core_error_background_report_kind,
     core_error_default_client_api_format, is_core_error_finalize_kind, LocalCoreSyncErrorKind,
 };
-use crate::gateway::ai_pipeline::private_response::normalize_provider_private_response_value as unwrap_local_finalize_response_value;
+use crate::gateway::api::response::build_client_response_from_parts;
 use crate::gateway::usage::spawn_sync_report;
 use crate::gateway::{
-    build_client_response_from_parts, maybe_compile_sync_finalize_response, AppState,
-    GatewayControlDecision, GatewayError, GatewaySyncReportRequest,
+    maybe_compile_sync_finalize_response, AppState, GatewayControlDecision, GatewayError,
+    GatewaySyncReportRequest,
 };
 use axum::body::Body;
 use axum::http::Response;