✨ 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_test.go

@@ -0,0 +1,113 @@
+package db
+
+import (
+	"strings"
+	"testing"
+
+	"GoNavi-Wails/internal/connection"
+)
+
+func TestGenerateChangePreview_Inserts(t *testing.T) {
+	changes := connection.ChangeSet{
+		Inserts: []map[string]interface{}{
+			{"name": "alice", "age": float64(30)},
+			{"name": "bob", "age": nil},
+		},
+	}
+	deletes, updates, inserts := GenerateChangePreview("users", changes, mysqlQuote)
+	if len(inserts) != 2 {
+		t.Fatalf("expected 2 inserts, got %d", len(inserts))
+	}
+	expected1 := "INSERT INTO `users` (`age`, `name`) VALUES (30, 'alice');"
+	expected2 := "INSERT INTO `users` (`name`) VALUES ('bob');"
+	if inserts[0] != expected1 {
+		t.Errorf("insert[0]: got  %s\nwant %s", inserts[0], expected1)
+	}
+	if inserts[1] != expected2 {
+		t.Errorf("insert[1]: got  %s\nwant %s", inserts[1], expected2)
+	}
+	if len(deletes) != 0 || len(updates) != 0 {
+		t.Errorf("expected empty deletes/updates")
+	}
+}
+
+func TestGenerateChangePreview_Deletes(t *testing.T) {
+	changes := connection.ChangeSet{
+		Deletes: []map[string]interface{}{
+			{"id": float64(1), "name": "alice"},
+			{"id": float64(2)},
+		},
+	}
+	deletes, updates, inserts := GenerateChangePreview("users", changes, mysqlQuote)
+	if len(deletes) != 2 {
+		t.Fatalf("expected 2 deletes, got %d", len(deletes))
+	}
+	expected1 := "DELETE FROM `users` WHERE `id` = 1 AND `name` = 'alice';"
+	if deletes[0] != expected1 {
+		t.Errorf("delete[0]: got  %s\nwant %s", deletes[0], expected1)
+	}
+	if len(updates) != 0 || len(inserts) != 0 {
+		t.Errorf("expected empty updates/inserts")
+	}
+}
+
+func TestGenerateChangePreview_Updates(t *testing.T) {
+	changes := connection.ChangeSet{
+		Updates: []connection.UpdateRow{
+			{
+				Keys:   map[string]interface{}{"id": float64(1)},
+				Values: map[string]interface{}{"name": "charlie", "age": float64(25)},
+			},
+		},
+	}
+	deletes, updates, inserts := GenerateChangePreview("users", changes, mysqlQuote)
+	if len(updates) != 1 {
+		t.Fatalf("expected 1 update, got %d", len(updates))
+	}
+	// SET clause column order is map-iteration-based, so check substring presence
+	if !strings.Contains(updates[0], "UPDATE `users` SET") {
+		t.Errorf("update: missing UPDATE clause: %s", updates[0])
+	}
+	if !strings.Contains(updates[0], "WHERE `id` = 1") {
+		t.Errorf("update: missing WHERE clause: %s", updates[0])
+	}
+	if !strings.Contains(updates[0], "`name` = 'charlie'") {
+		t.Errorf("update: missing name set: %s", updates[0])
+	}
+	if !strings.Contains(updates[0], "`age` = 25") {
+		t.Errorf("update: missing age set: %s", updates[0])
+	}
+	if len(deletes) != 0 || len(inserts) != 0 {
+		t.Errorf("expected empty deletes/inserts")
+	}
+}
+
+func TestGenerateChangePreview_EmptyChanges(t *testing.T) {
+	deletes, updates, inserts := GenerateChangePreview("t", connection.ChangeSet{}, mysqlQuote)
+	if len(deletes) != 0 || len(updates) != 0 || len(inserts) != 0 {
+		t.Error("expected all empty for empty changeset")
+	}
+}
+
+func TestFormatLiteral(t *testing.T) {
+	cases := []struct {
+		val      interface{}
+		expected string
+	}{
+		{nil, "NULL"},
+		{"hello", "'hello'"},
+		{"it's a test", "'it\\'s a test'"},
+		{float64(42), "42"},
+		{int64(-1), "-1"},
+		{true, "TRUE"},
+		{false, "FALSE"},
+	}
+	for _, c := range cases {
+		got := formatLiteral(c.val)
+		if got != c.expected {
+			t.Errorf("formatLiteral(%v): got %s, want %s", c.val, got, c.expected)
+		}
+	}
+}
+
+func mysqlQuote(s string) string { return "`" + s + "`" }