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/api/auth/__init__.py

@@ -0,0 +1,48 @@
+"""Authentication route group."""
+
+from __future__ import annotations
+
+from fastapi import APIRouter
+from starlette.routing import BaseRoute
+
+from .routes import router as auth_router
+
+_RUST_OWNED_AUTH_ROUTE_SIGNATURES = frozenset(
+    {
+        ("GET", "/api/auth/registration-settings"),
+        ("GET", "/api/auth/settings"),
+        ("POST", "/api/auth/login"),
+        ("POST", "/api/auth/refresh"),
+        ("POST", "/api/auth/register"),
+        ("GET", "/api/auth/me"),
+        ("POST", "/api/auth/logout"),
+        ("POST", "/api/auth/send-verification-code"),
+        ("POST", "/api/auth/verify-email"),
+        ("POST", "/api/auth/verification-status"),
+    }
+)
+
+
+def _route_is_rust_owned(route: BaseRoute) -> bool:
+    path = getattr(route, "path", None)
+    methods = getattr(route, "methods", None)
+    if not isinstance(path, str) or not methods:
+        return False
+    return any(
+        (method, path) in _RUST_OWNED_AUTH_ROUTE_SIGNATURES
+        for method in methods
+        if method not in {"HEAD", "OPTIONS"}
+    )
+
+
+def _build_python_auth_router() -> APIRouter:
+    router = APIRouter()
+    router.include_router(auth_router)
+    router.routes = [route for route in router.routes if not _route_is_rust_owned(route)]
+    return router
+
+
+python_auth_router = _build_python_auth_router()
+router = python_auth_router
+
+__all__ = ["python_auth_router", "router"]