✨ feat(data-grid): 增强数据表编辑与展示体验

- 新增变更预览能力，支持在提交前查看删除、更新和新增对应的 SQL 语句
- 增加表格密度配置，统一控制默认列宽、行高、字号与单元格内边距
- 优化 DataGrid 编辑状态展示，区分新增、修改和删除行列的视觉反馈
- 调整导出入口与 Wails 前端绑定，补齐变更预览相关调用与测试覆盖

frontend/wailsjs/go/app/App.d.ts

@@ -180,6 +180,8 @@ export function OpenDriverDownloadDirectory(arg1:string):Promise<connection.Quer
 
 export function OpenSQLFile():Promise<connection.QueryResult>;
 
+export function PreviewChanges(arg1:connection.ConnectionConfig,arg2:string,arg3:string,arg4:connection.ChangeSet):Promise<connection.QueryResult>;
+
 export function PreviewImportFile(arg1:string):Promise<connection.QueryResult>;
 
 export function ReadSQLFile(arg1:string):Promise<connection.QueryResult>;

frontend/wailsjs/go/app/App.js

@@ -350,6 +350,10 @@ export function OpenSQLFile() {
   return window['go']['app']['App']['OpenSQLFile']();
 }
 
+export function PreviewChanges(arg1, arg2, arg3, arg4) {
+  return window['go']['app']['App']['PreviewChanges'](arg1, arg2, arg3, arg4);
+}
+
 export function PreviewImportFile(arg1) {
   return window['go']['app']['App']['PreviewImportFile'](arg1);
 }