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/outcome_builder.py

@@ -0,0 +1,60 @@
+from __future__ import annotations
+
+from collections.abc import Callable
+from dataclasses import dataclass
+from typing import Any
+
+import httpx
+
+from src.services.billing.rule_service import BillingRuleLookupResult
+from src.services.candidate.submit import SubmitOutcome
+
+
+@dataclass(slots=True)
+class SubmitPayloadParseResult:
+    """提交响应解析结果。"""
+
+    payload: dict[str, Any] | None
+    error_type: str | None = None
+    error_message: str | None = None
+
+
+class AsyncSubmitOutcomeBuilderService:
+    """异步提交结果构建服务。"""
+
+    def __init__(self, *, sanitize: Callable[[str], str]) -> None:
+        self._sanitize = sanitize
+
+    def parse_payload(self, *, response: httpx.Response) -> SubmitPayloadParseResult:
+        payload: dict[str, Any] | None = None
+        try:
+            data = response.json()
+            if isinstance(data, dict):
+                payload = data
+        except Exception as exc:
+            return SubmitPayloadParseResult(
+                payload=None,
+                error_type=type(exc).__name__,
+                error_message=self._sanitize(str(exc)),
+            )
+        return SubmitPayloadParseResult(payload=payload)
+
+    @staticmethod
+    def build_success_outcome(
+        *,
+        candidate: Any,
+        candidate_keys: list[dict[str, Any]],
+        external_task_id: str,
+        rule_lookup: BillingRuleLookupResult | None,
+        payload: dict[str, Any] | None,
+        response: httpx.Response,
+    ) -> SubmitOutcome:
+        return SubmitOutcome(
+            candidate=candidate,
+            candidate_keys=candidate_keys,
+            external_task_id=external_task_id,
+            rule_lookup=rule_lookup,
+            upstream_payload=payload,
+            upstream_headers=dict(response.headers),
+            upstream_status_code=response.status_code,
+        )