✨ 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/db/change_preview.go

@@ -0,0 +1,135 @@
+package db
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+	"time"
+
+	"GoNavi-Wails/internal/connection"
+)
+
+// GenerateChangePreview 将 ChangeSet 转为可读 SQL 语句（不执行）。
+// quoteIdent 用于引用列名/表名（MySQL: backtick, PostgreSQL: double quote）。
+func GenerateChangePreview(tableName string, changes connection.ChangeSet, quoteIdent func(string) string) (deletes, updates, inserts []string) {
+	qt := quoteIdent
+
+	// Deletes
+	for _, pk := range changes.Deletes {
+		var conds []string
+		for _, k := range sortedKeys(pk) {
+			v := pk[k]
+			conds = append(conds, fmt.Sprintf("%s = %s", qt(k), formatLiteral(v)))
+		}
+		if len(conds) > 0 {
+			deletes = append(deletes, fmt.Sprintf("DELETE FROM %s WHERE %s;", qt(tableName), strings.Join(conds, " AND ")))
+		}
+	}
+
+	// Updates
+	for _, row := range changes.Updates {
+		var sets []string
+		for _, k := range sortedKeys(row.Values) {
+			v := row.Values[k]
+			sets = append(sets, fmt.Sprintf("%s = %s", qt(k), formatLiteral(v)))
+		}
+		if len(sets) == 0 {
+			continue
+		}
+		var conds []string
+		for _, k := range sortedKeys(row.Keys) {
+			v := row.Keys[k]
+			conds = append(conds, fmt.Sprintf("%s = %s", qt(k), formatLiteral(v)))
+		}
+		if len(conds) == 0 {
+			continue
+		}
+		updates = append(updates, fmt.Sprintf("UPDATE %s SET %s WHERE %s;", qt(tableName), strings.Join(sets, ", "), strings.Join(conds, " AND ")))
+	}
+
+	// Inserts
+	for _, row := range changes.Inserts {
+		var cols []string
+		var vals []string
+		for _, k := range sortedKeys(row) {
+			v := row[k]
+			if v == nil {
+				continue
+			}
+			cols = append(cols, qt(k))
+			vals = append(vals, formatLiteral(v))
+		}
+		if len(cols) == 0 {
+			continue
+		}
+		inserts = append(inserts, fmt.Sprintf("INSERT INTO %s (%s) VALUES (%s);", qt(tableName), strings.Join(cols, ", "), strings.Join(vals, ", ")))
+	}
+
+	return deletes, updates, inserts
+}
+
+// sortedKeys 返回 map 的键排序切片，保证输出确定性。
+func sortedKeys(m map[string]interface{}) []string {
+	keys := make([]string, 0, len(m))
+	for k := range m {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	return keys
+}
+
+// formatLiteral 将 Go 值转为 SQL 字面量字符串。
+func formatLiteral(v interface{}) string {
+	if v == nil {
+		return "NULL"
+	}
+	switch t := v.(type) {
+	case string:
+		escaped := strings.ReplaceAll(t, "\\", "\\\\")
+		escaped = strings.ReplaceAll(escaped, "'", "\\'")
+		return fmt.Sprintf("'%s'", escaped)
+	case float64:
+		return formatNumber(t)
+	case float32:
+		return formatNumber(float64(t))
+	case int:
+		return fmt.Sprintf("%d", t)
+	case int64:
+		return fmt.Sprintf("%d", t)
+	case int32:
+		return fmt.Sprintf("%d", t)
+	case int16:
+		return fmt.Sprintf("%d", t)
+	case int8:
+		return fmt.Sprintf("%d", t)
+	case uint64:
+		return fmt.Sprintf("%d", t)
+	case uint32:
+		return fmt.Sprintf("%d", t)
+	case uint16:
+		return fmt.Sprintf("%d", t)
+	case uint8:
+		return fmt.Sprintf("%d", t)
+	case uint:
+		return fmt.Sprintf("%d", t)
+	case time.Time:
+		return fmt.Sprintf("'%s'", t.Format("2006-01-02 15:04:05"))
+	case bool:
+		if t {
+			return "TRUE"
+		}
+		return "FALSE"
+	case []byte:
+		return formatLiteral(string(t))
+	default:
+		escaped := strings.ReplaceAll(fmt.Sprintf("%v", t), "'", "\\'")
+		return fmt.Sprintf("'%s'", escaped)
+	}
+}
+
+func formatNumber(f float64) string {
+	if f == float64(int64(f)) {
+		return fmt.Sprintf("%d", int64(f))
+	}
+	return fmt.Sprintf("%v", f)
+}