🐛 fix(external-sql): 修复外部 SQL 文件保存不写回源文件

- 保存逻辑：外部 SQL 文件标签页携带 filePath，保存时写回原始磁盘文件
- 后端接口：新增 WriteSQLFile 能力，支持覆盖已有 SQL 文件并保留原文件权限
- 状态隔离：外部文件保存失败时不创建 savedQuery，避免写入 localStorage 副本
- 兼容行为：非文件标签页继续沿用原有 savedQuery 快速保存逻辑
- 文案优化：将数据库下入口改为“外部 SQL 目录”，减少与单文件打开入口的歧义
- 测试覆盖：补充前端保存分支、后端写文件边界和外部 SQL 目录文案测试
Refs #422

internal/app/methods_file.go

@@ -96,6 +96,29 @@ func readSQLFileByPath(filePath string) connection.QueryResult {
 	return connection.QueryResult{Success: true, Data: string(content)}
 }
 
+func writeSQLFileByPath(filePath string, content string) connection.QueryResult {
+	target := strings.TrimSpace(filePath)
+	if target == "" {
+		return connection.QueryResult{Success: false, Message: "文件路径不能为空"}
+	}
+	if abs, err := filepath.Abs(target); err == nil {
+		target = abs
+	}
+
+	info, err := os.Stat(target)
+	if err != nil {
+		return connection.QueryResult{Success: false, Message: fmt.Sprintf("无法读取文件信息: %v", err)}
+	}
+	if info.IsDir() {
+		return connection.QueryResult{Success: false, Message: "所选路径不是 SQL 文件"}
+	}
+
+	if err := os.WriteFile(target, []byte(content), info.Mode().Perm()); err != nil {
+		return connection.QueryResult{Success: false, Message: fmt.Sprintf("无法写入 SQL 文件: %v", err)}
+	}
+	return connection.QueryResult{Success: true, Data: map[string]interface{}{"filePath": target}}
+}
+
 func buildSQLDirectoryEntries(directory string) ([]SQLDirectoryEntry, error) {
 	entries, err := os.ReadDir(directory)
 	if err != nil {
@@ -215,6 +238,10 @@ func (a *App) ReadSQLFile(filePath string) connection.QueryResult {
 	return readSQLFileByPath(filePath)
 }
 
+func (a *App) WriteSQLFile(filePath string, content string) connection.QueryResult {
+	return writeSQLFileByPath(filePath, content)
+}
+
 // ExecuteSQLFile 在后端流式读取并执行大 SQL 文件，通过事件推送进度。
 // 前端通过 EventsOn("sqlfile:progress", ...) 监听进度。
 func (a *App) ExecuteSQLFile(config connection.ConnectionConfig, dbName string, filePath string, jobID string) connection.QueryResult {

internal/app/methods_file_sql_directory_test.go

@@ -41,6 +41,40 @@ func TestBuildSQLDirectoryEntriesKeepsOnlySQLFilesAndNestedFolders(t *testing.T)
 	}
 }
 
+func TestWriteSQLFileByPathOverwritesExistingSQLFile(t *testing.T) {
+	filePath := filepath.Join(t.TempDir(), "report.sql")
+	if err := os.WriteFile(filePath, []byte("select 1;"), 0o644); err != nil {
+		t.Fatalf("WriteFile returned error: %v", err)
+	}
+
+	result := writeSQLFileByPath(filePath, "select 2;\n")
+	if !result.Success {
+		t.Fatalf("expected sql file write to succeed, got %#v", result)
+	}
+
+	content, err := os.ReadFile(filePath)
+	if err != nil {
+		t.Fatalf("ReadFile returned error: %v", err)
+	}
+	if string(content) != "select 2;\n" {
+		t.Fatalf("expected file content to be overwritten, got %q", string(content))
+	}
+}
+
+func TestWriteSQLFileByPathRejectsDirectories(t *testing.T) {
+	result := writeSQLFileByPath(t.TempDir(), "select 1;")
+	if result.Success {
+		t.Fatalf("expected directory write to fail, got %#v", result)
+	}
+}
+
+func TestWriteSQLFileByPathRejectsEmptyPath(t *testing.T) {
+	result := writeSQLFileByPath("   ", "select 1;")
+	if result.Success {
+		t.Fatalf("expected empty path write to fail, got %#v", result)
+	}
+}
+
 func TestReadSQLFileByPathReturnsLargeFileMetadata(t *testing.T) {
 	filePath := filepath.Join(t.TempDir(), "big.sql")
 	file, err := os.Create(filePath)