refactor: 移除备份恢复功能(API/CLI/手册)

日志数据的保留与安全由对象存储 + Loki retention 承担,平台侧整库备份恢复价值有限:
删除 services/backup.go、/system/{backup,restore,restore/apply,backups} 路由与 handler、
CLI backup/restore 子命令、前端 api 方法与类型;自检所需的 dataDirPath/密钥指纹并入 selfcheck;
用户手册删备份章节并修正 FAQ 升级建议;CHANGELOG 记录移除。

frontend/src/api/system/index.ts

@@ -65,27 +65,6 @@ export interface SelfCheckResult {
   items: SelfCheckItem[];
 }
 
-export interface BackupFile {
-  name: string;
-  sizeBytes: number;
-  createdAt: string;
-}
-
-export interface RestoreResult {
-  manifest: {
-    version: string;
-    createdAt: string;
-    dbBytes: number;
-    recordCount: number;
-    note: string;
-  };
-  keyMatches: boolean;
-  rowsInBackup: number;
-  currentRows: number;
-  stagedPath?: string;
-  warning?: string;
-}
-
 export const systemApi = {
   // 审计
   auditList: (params: AuditListParams = {}, opts?: { signal?: AbortSignal }) =>
@@ -99,16 +78,6 @@ export const systemApi = {
   // 自检
   selfCheck: () => http.get<SelfCheckResult>('/system/self-check'),
 
-  // 备份恢复
-  backups: () => http.get<{ list: BackupFile[] }>('/system/backups'),
-  restore: (file: File) => {
-    const form = new FormData();
-    form.append('file', file);
-    return http.post<RestoreResult>('/system/restore', form);
-  },
-  restoreApply: () =>
-    http.post<{ message: string; dbPath: string }>('/system/restore/apply', { confirm: true }),
-
   // 平台数据保留期（告警发送历史 / 审计日志）
   retention: () => http.get<RetentionSettings>('/settings/retention'),
   saveRetention: (data: RetentionSettings) => http.put<RetentionSettings>('/settings/retention', data),