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/user/bulk_cleanup.py

@@ -0,0 +1,111 @@
+from __future__ import annotations
+
+import time
+from typing import Any
+
+from sqlalchemy.orm import Session
+
+from src.core.logger import logger
+from src.models.database import RequestCandidate, Usage
+
+_POSTGRES_BATCH_SIZE = 2000
+_SQLITE_BATCH_SIZE = 900
+
+
+def _resolve_batch_size(db: Session) -> int:
+    try:
+        bind = db.get_bind()
+        dialect_name = str(getattr(getattr(bind, "dialect", None), "name", "") or "").lower()
+    except Exception:
+        dialect_name = ""
+
+    if dialect_name == "sqlite":
+        return _SQLITE_BATCH_SIZE
+    return _POSTGRES_BATCH_SIZE
+
+
+def batch_nullify_fk(
+    db: Session,
+    model: type[Any],
+    column_name: str,
+    entity_id: str | None,
+) -> int:
+    """分批将大表外键置空，避免单个长事务阻塞删除流程。"""
+    if not entity_id:
+        return 0
+
+    column = getattr(model, column_name)
+    primary_key_column = next(iter(model.__table__.primary_key.columns))
+    batch_size = _resolve_batch_size(db)
+    total_updated = 0
+    batch_index = 0
+    started_at = time.monotonic()
+
+    while True:
+        batch_ids = [
+            row[0]
+            for row in db.query(primary_key_column)
+            .filter(column == entity_id)
+            .limit(batch_size)
+            .all()
+        ]
+        if not batch_ids:
+            break
+
+        batch_index += 1
+        batch_started_at = time.monotonic()
+        updated = int(
+            db.query(model)
+            .filter(primary_key_column.in_(batch_ids))
+            .update({column: None}, synchronize_session=False)
+            or 0
+        )
+        db.commit()
+
+        total_updated += updated
+        elapsed_ms = int((time.monotonic() - batch_started_at) * 1000)
+        logger.info(
+            "批量清理 {}.{}: batch={}, updated={}, entity_id={}, elapsed_ms={}",
+            model.__tablename__,
+            column_name,
+            batch_index,
+            updated,
+            entity_id,
+            elapsed_ms,
+        )
+
+        if len(batch_ids) < batch_size:
+            break
+
+    if total_updated > 0:
+        total_elapsed_ms = int((time.monotonic() - started_at) * 1000)
+        logger.info(
+            "批量清理完成 {}.{}: total_updated={}, entity_id={}, elapsed_ms={}",
+            model.__tablename__,
+            column_name,
+            total_updated,
+            entity_id,
+            total_elapsed_ms,
+        )
+
+    return total_updated
+
+
+def pre_clean_api_key(db: Session, api_key_id: str | None) -> int:
+    """预清理 API Key 在大表中的外键引用，减少后续删除锁竞争。"""
+    if not api_key_id:
+        return 0
+
+    usage_rows = batch_nullify_fk(db, Usage, "api_key_id", api_key_id)
+    candidate_rows = batch_nullify_fk(db, RequestCandidate, "api_key_id", api_key_id)
+    total_rows = usage_rows + candidate_rows
+
+    if total_rows > 0:
+        logger.info(
+            "API Key 预清理完成: api_key_id={}, usage={}, request_candidates={}",
+            api_key_id,
+            usage_rows,
+            candidate_rows,
+        )
+
+    return total_rows