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)

_deprecated_py_src/services/auth/refresh_cookie.py

@@ -0,0 +1,35 @@
+from __future__ import annotations
+
+from starlette.responses import Response
+
+from src.config import config
+from src.core.exceptions import ErrorResponse
+from src.services.auth.service import REFRESH_TOKEN_EXPIRATION_DAYS
+
+
+def set_refresh_token_cookie(response: Response, refresh_token: str) -> None:
+    max_age_seconds = REFRESH_TOKEN_EXPIRATION_DAYS * 24 * 60 * 60
+    response.set_cookie(
+        key=config.auth_refresh_cookie_name,
+        value=refresh_token,
+        httponly=True,
+        secure=config.auth_refresh_cookie_secure,
+        samesite=config.auth_refresh_cookie_samesite,
+        path="/api/auth",
+        max_age=max_age_seconds,
+    )
+
+
+def clear_refresh_token_cookie(response: Response) -> None:
+    response.delete_cookie(
+        key=config.auth_refresh_cookie_name,
+        path="/api/auth",
+        secure=config.auth_refresh_cookie_secure,
+        samesite=config.auth_refresh_cookie_samesite,
+    )
+
+
+def error_response_with_cleared_cookie(exc: Exception) -> Response:
+    response = ErrorResponse.from_exception(exc)
+    clear_refresh_token_cookie(response)
+    return response