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/execute.py

@@ -0,0 +1,104 @@
+from __future__ import annotations
+
+from collections.abc import Callable
+from typing import Any
+
+import httpx
+from sqlalchemy.orm import Session
+
+from src.config.settings import config
+from src.services.candidate.submit import AllCandidatesFailedError, SubmitOutcome
+from src.services.task.submit.attempt import AsyncSubmitAttemptService
+from src.services.task.submit.filter import AsyncSubmitFilterService
+
+
+class AsyncSubmitExecutionService:
+    """异步提交候选执行编排服务。"""
+
+    def __init__(
+        self,
+        db: Session,
+        *,
+        sanitize: Callable[[str], str],
+        extract_response_text: Callable[[httpx.Response], str],
+        match_provider_failover_rule: Callable[..., str | None],
+    ) -> None:
+        self.db = db
+        self._filter_ops = AsyncSubmitFilterService(db)
+        self._attempt_ops = AsyncSubmitAttemptService(
+            db,
+            sanitize=sanitize,
+            extract_response_text=extract_response_text,
+            match_provider_failover_rule=match_provider_failover_rule,
+        )
+
+    async def execute_submit_loop(
+        self,
+        *,
+        candidates: list[Any],
+        record_map: dict[tuple[int, int], str],
+        task_type: str,
+        model_name: str,
+        submit_func: Any,
+        extract_external_task_id: Any,
+        supported_auth_types: set[str] | None,
+        allow_format_conversion: bool,
+    ) -> SubmitOutcome:
+        candidate_keys: list[dict[str, Any]] = []
+        eligible_count = 0
+        last_status_code: int | None = None
+
+        for idx, cand in enumerate(candidates):
+            candidate_info = self._filter_ops.build_candidate_info(idx=idx, candidate=cand)
+            candidate_keys.append(candidate_info)
+
+            attempt_plan = self._filter_ops.prepare_candidate_for_attempt(
+                idx=idx,
+                candidate=cand,
+                record_map=record_map,
+                candidate_info=candidate_info,
+                task_type=task_type,
+                model_name=model_name,
+                supported_auth_types=supported_auth_types,
+                allow_format_conversion=allow_format_conversion,
+            )
+            if attempt_plan is None:
+                continue
+
+            eligible_count += 1
+            outcome, status_code = await self._attempt_ops.submit_candidate(
+                candidate=cand,
+                record_id=attempt_plan.record_id,
+                candidate_info=candidate_info,
+                candidate_keys=candidate_keys,
+                rule_lookup=attempt_plan.rule_lookup,
+                submit_func=submit_func,
+                extract_external_task_id=extract_external_task_id,
+            )
+
+            if status_code is not None:
+                last_status_code = status_code
+            if outcome is not None:
+                return outcome
+
+        # Persist candidate records before raising.
+        try:
+            self.db.commit()
+        except Exception:
+            self.db.rollback()
+
+        if eligible_count == 0:
+            reason = "no_eligible_candidates"
+            if config.billing_require_rule:
+                reason = "no_candidate_with_billing_rule"
+            raise AllCandidatesFailedError(
+                reason=reason,
+                candidate_keys=candidate_keys,
+                last_status_code=last_status_code,
+            )
+
+        raise AllCandidatesFailedError(
+            reason="all_candidates_failed",
+            candidate_keys=candidate_keys,
+            last_status_code=last_status_code,
+        )