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/task/request_state.py

@@ -0,0 +1,64 @@
+from __future__ import annotations
+
+import copy
+from dataclasses import dataclass, field
+from typing import Any, Protocol
+
+
+class RequestBodyState(Protocol):
+    @property
+    def current_body(self) -> dict[str, Any]: ...
+
+    def build_attempt_body(self) -> dict[str, Any]: ...
+
+    def is_rectified(self) -> bool: ...
+
+    def rectify_stage(self) -> int: ...
+
+    def mark_rectified(self, body: dict[str, Any], *, stage: int) -> None: ...
+
+    def consume_rectified_this_turn(self) -> bool: ...
+
+
+@dataclass(slots=True)
+class MutableRequestBodyState:
+    """Owns the mutable working request body used across retries."""
+
+    original_body: dict[str, Any]
+    _current_body: dict[str, Any] = field(init=False, repr=False)
+    _rectified: bool = field(default=False, init=False, repr=False)
+    _rectified_this_turn: bool = field(default=False, init=False, repr=False)
+    _rectify_stage: int = field(default=0, init=False, repr=False)
+
+    def __post_init__(self) -> None:
+        # Attempts already deep-copy per dispatch, and rectification paths clone before
+        # rewriting. Keep the initial working body as a direct view to avoid an eager copy.
+        self._current_body = self.original_body
+
+    @property
+    def current_body(self) -> dict[str, Any]:
+        return self._current_body
+
+    def build_attempt_body(self) -> dict[str, Any]:
+        return copy.deepcopy(self._current_body)
+
+    def is_rectified(self) -> bool:
+        return self._rectified
+
+    def rectify_stage(self) -> int:
+        return self._rectify_stage
+
+    def mark_rectified(self, body: dict[str, Any], *, stage: int) -> None:
+        self._current_body = body
+        self._rectified = True
+        self._rectified_this_turn = True
+        self._rectify_stage = stage
+
+    def consume_rectified_this_turn(self) -> bool:
+        if not self._rectified_this_turn:
+            return False
+        self._rectified_this_turn = False
+        return True
+
+
+__all__ = ["MutableRequestBodyState", "RequestBodyState"]