✨ feat(sync): 新增 SQL 结果集数据同步能力

- 同步引擎新增查询结果集同步分支，支持单目标表差异分析、预览与执行
- 数据同步工作台增加 SQL 结果集模式，并补充目标表与查询校验
- 补充后端同步链路与前端请求构造回归测试，并更新 backlog 记录

Fixes #321

frontend/src/components/dataSyncRequest.ts

@@ -0,0 +1,85 @@
+export type SourceDatasetMode = 'table' | 'query';
+
+type SyncContent = 'data' | 'schema' | 'both';
+type TargetTableStrategy = 'existing_only' | 'auto_create_if_missing' | 'smart';
+
+type BuildDataSyncRequestParams = {
+  sourceConfig: any;
+  targetConfig: any;
+  selectedTables: string[];
+  sourceDatasetMode: SourceDatasetMode;
+  sourceQuery: string;
+  syncContent: SyncContent;
+  syncMode: string;
+  autoAddColumns: boolean;
+  targetTableStrategy: TargetTableStrategy;
+  createIndexes: boolean;
+  mongoCollectionName: string;
+  jobId?: string;
+  tableOptions?: Record<string, any>;
+};
+
+type ValidateDataSyncSelectionParams = {
+  sourceDatasetMode: SourceDatasetMode;
+  selectedTables: string[];
+  sourceQuery: string;
+  syncContent: SyncContent;
+};
+
+export const validateDataSyncSelection = ({
+  sourceDatasetMode,
+  selectedTables,
+  sourceQuery,
+  syncContent,
+}: ValidateDataSyncSelectionParams): string | null => {
+  if (sourceDatasetMode === 'query') {
+    if (!String(sourceQuery || '').trim()) {
+      return '请输入源查询 SQL';
+    }
+    if (selectedTables.length !== 1) {
+      return 'SQL 结果集同步需要选择一个目标表';
+    }
+    if (syncContent !== 'data') {
+      return 'SQL 结果集同步仅支持仅同步数据';
+    }
+    return null;
+  }
+
+  if (selectedTables.length === 0) {
+    return '请选择至少一张表';
+  }
+  return null;
+};
+
+export const buildDataSyncRequest = ({
+  sourceConfig,
+  targetConfig,
+  selectedTables,
+  sourceDatasetMode,
+  sourceQuery,
+  syncContent,
+  syncMode,
+  autoAddColumns,
+  targetTableStrategy,
+  createIndexes,
+  mongoCollectionName,
+  jobId,
+  tableOptions,
+}: BuildDataSyncRequestParams) => {
+  const isQueryMode = sourceDatasetMode === 'query';
+
+  return {
+    sourceConfig,
+    targetConfig,
+    tables: selectedTables,
+    sourceQuery: isQueryMode ? String(sourceQuery || '').trim() : undefined,
+    content: isQueryMode ? 'data' : syncContent,
+    mode: syncMode,
+    autoAddColumns: isQueryMode ? false : autoAddColumns,
+    targetTableStrategy: isQueryMode ? 'existing_only' : targetTableStrategy,
+    createIndexes: isQueryMode ? false : createIndexes,
+    mongoCollectionName: String(mongoCollectionName || '').trim(),
+    ...(jobId ? { jobId } : {}),
+    ...(tableOptions ? { tableOptions } : {}),
+  };
+};