✨ 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

internal/app/methods_file.go

@@ -1012,6 +1012,35 @@ func (a *App) ApplyChanges(config connection.ConnectionConfig, dbName, tableName
 	return connection.QueryResult{Success: false, Message: "当前数据库类型不支持批量提交"}
 }
 
+// ChangePreview 变更预览结果
+type ChangePreview struct {
+	Deletes []string `json:"deletes"`
+	Updates []string `json:"updates"`
+	Inserts []string `json:"inserts"`
+}
+
+func (a *App) PreviewChanges(config connection.ConnectionConfig, dbName, tableName string, changes connection.ChangeSet) connection.QueryResult {
+	runConfig := normalizeRunConfig(config, dbName)
+
+	dbInst, err := a.getDatabase(runConfig)
+	if err != nil {
+		return connection.QueryResult{Success: false, Message: err.Error()}
+	}
+
+	var cp ChangePreview
+	// 优先使用驱动的 PreviewChanges（若实现了 ChangePreviewer 接口）
+	if previewer, ok := dbInst.(db.ChangePreviewer); ok {
+		deletes, updates, inserts := previewer.PreviewChanges(tableName, changes)
+		cp = ChangePreview{Deletes: deletes, Updates: updates, Inserts: inserts}
+	} else {
+		// 回退到通用生成，使用 quoteIdentByType 处理标识符转义
+		quoter := func(s string) string { return quoteIdentByType(runConfig.Type, s) }
+		deletes, updates, inserts := db.GenerateChangePreview(tableName, changes, quoter)
+		cp = ChangePreview{Deletes: deletes, Updates: updates, Inserts: inserts}
+	}
+	return connection.QueryResult{Success: true, Data: cp}
+}
+
 func (a *App) ExportTable(config connection.ConnectionConfig, dbName string, tableName string, format string) connection.QueryResult {
 	filename, err := runtime.SaveFileDialog(a.ctx, runtime.SaveDialogOptions{
 		Title:           fmt.Sprintf("Export %s", tableName),