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/provider/pool/hooks.py

@@ -0,0 +1,91 @@
+"""Pool scheduling hooks -- provider-type-specific pool behaviour.
+
+Some provider types need custom logic during pool scheduling (e.g. extracting
+a session UUID for sticky binding).  This module provides a small Protocol +
+registry so the pool layer stays generic while provider-specific behaviour
+lives alongside each adapter.
+"""
+
+from __future__ import annotations
+
+import threading
+from typing import Any, Protocol, runtime_checkable
+
+# ---------------------------------------------------------------------------
+# Protocol
+# ---------------------------------------------------------------------------
+
+
+@runtime_checkable
+class PoolSchedulingHook(Protocol):
+    """Provider-type-specific pool scheduling behaviour.
+
+    Each provider type can optionally register a hook to customize:
+    - Session UUID extraction (for sticky sessions)
+    - Post-success / post-error callbacks
+
+    Optional methods (checked via ``hasattr`` by callers):
+    - ``on_pool_success``
+    - ``on_pool_error``
+    """
+
+    name: str
+
+    def extract_session_uuid(self, request_body: dict[str, Any]) -> str | None:
+        """Extract a session UUID for sticky binding from the request body."""
+        ...
+
+    # -- Optional lifecycle callbacks -----------------------------------------
+    # These are checked via ``hasattr`` so existing implementations that
+    # don't define them will continue to work.
+
+    def on_pool_success(
+        self,
+        *,
+        key_id: str,
+        session_uuid: str | None,
+        context: dict[str, Any],
+    ) -> None:
+        """Called after a successful pool request (provider-specific logic)."""
+        ...
+
+    def on_pool_error(
+        self,
+        *,
+        key_id: str,
+        status_code: int,
+        context: dict[str, Any],
+    ) -> None:
+        """Called after a failed pool request (provider-specific logic)."""
+        ...
+
+
+# ---------------------------------------------------------------------------
+# Registry
+# ---------------------------------------------------------------------------
+
+_hook_registry: dict[str, PoolSchedulingHook] = {}
+_registry_lock = threading.Lock()
+
+
+def register_pool_hook(provider_type: str, hook: PoolSchedulingHook) -> None:
+    """Register a pool scheduling hook for a provider type."""
+    from src.core.provider_types import normalize_provider_type
+
+    pt = normalize_provider_type(provider_type)
+    with _registry_lock:
+        _hook_registry[pt] = hook
+
+
+def get_pool_hook(provider_type: str | None) -> PoolSchedulingHook | None:
+    """Return the pool scheduling hook for a provider type, or ``None``."""
+    if not provider_type:
+        return None
+    from src.services.provider.envelope import ensure_providers_bootstrapped
+
+    ensure_providers_bootstrapped(provider_types=[provider_type])
+
+    from src.core.provider_types import normalize_provider_type
+
+    pt = normalize_provider_type(provider_type)
+    return _hook_registry.get(pt)