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)

frontend/src/pages/PlatformConfigPage.tsx

@@ -15,11 +15,75 @@ interface SettingItem {
 
 type SettingsMap = Record<string, SettingItem[]>;
 
+/* ── 清理操作子组件 ── */
+function CleanupActions() {
+  const [preview, setPreview] = useState<Record<string, number> | null>(null);
+  const [loading, setLoading] = useState(false);
+  const [cleaning, setCleaning] = useState(false);
+  const [result, setResult] = useState<string>('');
+
+  const handlePreview = async () => {
+    setLoading(true);
+    setResult('');
+    try {
+      const res = await api.get('/settings/cleanup/preview') as Record<string, number>;
+      setPreview(res);
+    } catch {
+      setResult('预览失败');
+    } finally {
+      setLoading(false);
+    }
+  };
+
+  const handleCleanup = async () => {
+    setCleaning(true);
+    setResult('');
+    try {
+      const res = await api.post('/settings/cleanup/run') as { message: string; stats: Record<string, number> };
+      const total = Object.values(res.stats).reduce((a, b) => a + b, 0);
+      setResult(`清理完成，共删除 ${total} 条记录`);
+      setPreview(null);
+    } catch {
+      setResult('清理失败');
+    } finally {
+      setCleaning(false);
+    }
+  };
+
+  return (
+    <div className="px-5 pb-4 pt-2 space-y-3">
+      <div className="flex items-center gap-3">
+        <button onClick={handlePreview} disabled={loading}
+          className="px-4 py-1.5 rounded-lg text-sm bg-[var(--dg-bg-tertiary)] text-[var(--dg-text-primary)] hover:bg-[var(--dg-bg-hover)] disabled:opacity-50 transition-colors">
+          {loading ? '查询中...' : '预览待清理数量'}
+        </button>
+        {preview && (
+          <button onClick={handleCleanup} disabled={cleaning}
+            className="px-4 py-1.5 rounded-lg text-sm bg-orange-500 hover:bg-orange-600 text-white disabled:opacity-50 transition-colors">
+            {cleaning ? '清理中...' : '立即清理'}
+          </button>
+        )}
+      </div>
+      {preview && (
+        <div className="text-xs text-[var(--dg-text-muted)] space-y-1">
+          {Object.entries(preview).map(([k, v]) => (
+            <div key={k}>{k}: <span className="text-[var(--dg-text-primary)] font-medium">{v}</span> 条</div>
+          ))}
+        </div>
+      )}
+      {result && (
+        <div className="text-xs text-emerald-500">{result}</div>
+      )}
+    </div>
+  );
+}
+
 /* ── 分组元信息 ── */
 const GROUP_META: Record<string, { label: string; icon: string; desc: string }> = {
   query: { label: '查询控制', icon: '🔍', desc: '查询权限、LIMIT 上限、超时设置' },
   security: { label: '安全策略', icon: '🔒', desc: '登录安全、密码策略、审计日志' },
   ticket: { label: '工单流程', icon: '📋', desc: '审批流程、回滚控制' },
+  cleanup: { label: '日志清理', icon: '🧹', desc: '数据变更工单、审计日志、查询历史的自动清理策略' },
 };
 
 export default function PlatformConfigPage() {
@@ -179,6 +243,9 @@ export default function PlatformConfigPage() {
                 );
               })}
             </div>
+
+            {/* 日志清理分组专属操作区 */}
+            {group === 'cleanup' && <CleanupActions />}
           </div>
         );
       })}