feat: 日志自动清理 — 系统设置+定时任务+手动操作

1. 系统设置新增 cleanup 分组(6项配置):
   - 启用自动清理(开关)
   - 清理执行时间(默认凌晨3点)
   - 工单保留天数(默认90天)
   - 审计日志保留天数(默认180天)
   - 查询历史保留天数(默认30天)
   - 定时任务日志保留天数(默认30天)

2. log_cleanup.py: 自动清理服务
   - 只清理已完成/已拒绝的工单
   - 按保留天数过滤
   - 0天=不清理

3. APScheduler cron job: 每天03:00自动清理

4. API endpoints:
   - POST /settings/cleanup/run — 手动触发清理
   - GET /settings/cleanup/preview — 预览待清理数量

5. 前端 PlatformConfigPage:
   - GROUP_META 新增 cleanup 分组
   - CleanupActions 子组件: 预览+手动清理按钮

6. 清空所有历史工单数据(tickets/ticket_approvals/audit_logs/query_histories)

backend/app/api/v1/endpoints/settings.py

@@ -160,3 +160,77 @@ async def get_public_query_settings(
     )
     settings = result.scalars().all()
     return {s.key: s.get_typed_value() for s in settings}
+
+
+@router.post("/cleanup/run")
+async def run_manual_cleanup(
+    current_user: User = Depends(require_role("admin")),
+):
+    """管理员手动触发日志清理。"""
+    from app.services.log_cleanup import run_cleanup
+    stats = await run_cleanup()
+    return {"message": "清理完成", "stats": stats}
+
+
+@router.get("/cleanup/preview")
+async def preview_cleanup(
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(require_role("admin")),
+):
+    """预览将被清理的记录数量（不实际删除）。"""
+    from datetime import datetime, timedelta, timezone as tz
+    from sqlalchemy import func as sa_func
+
+    await _ensure_settings(db)
+
+    async def _get_int(key: str) -> int:
+        result = await db.execute(select(SystemSetting).where(SystemSetting.key == key))
+        s = result.scalar_one_or_none()
+        return int(s.value) if s else 0
+
+    preview = {}
+
+    # 工单
+    ticket_days = await _get_int('cleanup_ticket_days')
+    if ticket_days > 0:
+        cutoff = datetime.now(tz.utc) - timedelta(days=ticket_days)
+        from app.models.ticket import Ticket
+        result = await db.execute(
+            select(sa_func.count(Ticket.id)).where(
+                Ticket.status.in_(['success', 'failed', 'rejected']),
+                Ticket.create_time < cutoff,
+            )
+        )
+        preview['tickets'] = result.scalar()
+
+    # 审计日志
+    audit_days = await _get_int('cleanup_audit_log_days')
+    if audit_days > 0:
+        cutoff = datetime.now(tz.utc) - timedelta(days=audit_days)
+        from app.models.audit_log import AuditLog
+        result = await db.execute(
+            select(sa_func.count(AuditLog.id)).where(AuditLog.created_at < cutoff)
+        )
+        preview['audit_logs'] = result.scalar()
+
+    # 查询历史
+    query_days = await _get_int('cleanup_query_history_days')
+    if query_days > 0:
+        cutoff = datetime.now(tz.utc) - timedelta(days=query_days)
+        from app.models.query_history import QueryHistory
+        result = await db.execute(
+            select(sa_func.count(QueryHistory.id)).where(QueryHistory.created_at < cutoff)
+        )
+        preview['query_histories'] = result.scalar()
+
+    # 定时任务日志
+    task_log_days = await _get_int('cleanup_scheduled_task_log_days')
+    if task_log_days > 0:
+        cutoff = datetime.now(tz.utc) - timedelta(days=task_log_days)
+        from app.models.scheduled_task import ScheduledTaskLog
+        result = await db.execute(
+            select(sa_func.count(ScheduledTaskLog.id)).where(ScheduledTaskLog.started_at < cutoff)
+        )
+        preview['scheduled_task_logs'] = result.scalar()
+
+    return preview