feat(backup): 新增备份内容浏览 (#90)

查看每次备份捕获的文件清单（路径/大小/目录），核对完整性、排查遗漏。清单取自全量备份记录，无需下载解压；差异记录回退基线清单。只读端点 + 前端可筛选弹窗。

server/internal/http/backup_record_handler.go

@@ -52,6 +52,20 @@ func (h *BackupRecordHandler) Get(c *gin.Context) {
 	response.Success(c, item)
 }
 
+// Contents 返回备份记录的文件清单（内容浏览，只读）。
+func (h *BackupRecordHandler) Contents(c *gin.Context) {
+	id, ok := parseUintParam(c, "id")
+	if !ok {
+		return
+	}
+	contents, err := h.service.ListContents(c.Request.Context(), id)
+	if err != nil {
+		response.Error(c, err)
+		return
+	}
+	response.Success(c, contents)
+}
+
 func (h *BackupRecordHandler) StreamLogs(c *gin.Context) {
 	id, ok := parseUintParam(c, "id")
 	if !ok {

server/internal/http/router.go

@@ -167,6 +167,7 @@ func NewRouter(deps RouterDependencies) *gin.Engine {
 		backupRecords.GET("/:id", backupRecordHandler.Get)
 		backupRecords.GET("/:id/logs/stream", backupRecordHandler.StreamLogs)
 		backupRecords.GET("/:id/download", backupRecordHandler.Download)
+		backupRecords.GET("/:id/contents", backupRecordHandler.Contents)
 		backupRecords.POST("/:id/restore", RequireNotViewer(), backupRecordHandler.Restore)
 		backupRecords.POST("/batch-delete", RequireNotViewer(), backupRecordHandler.BatchDelete)
 		backupRecords.DELETE("/:id", RequireNotViewer(), backupRecordHandler.Delete)