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/submit/rule_decider.py

@@ -0,0 +1,43 @@
+from __future__ import annotations
+
+from collections.abc import Callable
+from typing import Any
+
+
+class AsyncSubmitRuleDeciderService:
+    """异步提交故障转移规则判定服务。"""
+
+    def __init__(
+        self,
+        *,
+        match_provider_failover_rule: Callable[..., str | None],
+    ) -> None:
+        self._match_provider_failover_rule = match_provider_failover_rule
+
+    def detect_error_stop_pattern(
+        self,
+        *,
+        candidate: Any,
+        response_text: str,
+        status_code: int,
+    ) -> str | None:
+        return self._match_provider_failover_rule(
+            candidate,
+            is_success=False,
+            response_text=response_text,
+            status_code=status_code,
+        )
+
+    def detect_success_failover_pattern(
+        self,
+        *,
+        candidate: Any,
+        response_text: str,
+        status_code: int,
+    ) -> str | None:
+        return self._match_provider_failover_rule(
+            candidate,
+            is_success=True,
+            response_text=response_text,
+            status_code=status_code,
+        )