✨ feat(postgres): 新增数据库节点新建模式功能

- 后端新增 CreateSchema 接口，支持在选中 PostgreSQL 数据库下创建 schema

- 侧边栏旧版菜单和新版菜单均增加新建模式入口

- 创建成功后刷新对象树，并支持空模式显示

- 补充 Wails 绑定与创建模式相关测试

Refs #480

internal/app/methods_db.go

@@ -149,6 +149,56 @@ func (a *App) CreateDatabase(config connection.ConnectionConfig, dbName string)
 	return connection.QueryResult{Success: true, Message: "数据库创建成功"}
 }
 
+func isPostgresSchemaDDLDBType(dbType string) bool {
+	switch resolveDDLDBType(connection.ConnectionConfig{Type: dbType}) {
+	case "postgres", "kingbase", "highgo", "vastbase", "opengauss":
+		return true
+	default:
+		return false
+	}
+}
+
+func buildCreateSchemaSQL(dbType string, schemaName string) (string, error) {
+	schemaName = strings.TrimSpace(schemaName)
+	if schemaName == "" {
+		return "", fmt.Errorf("模式名称不能为空")
+	}
+
+	if !isPostgresSchemaDDLDBType(dbType) {
+		return "", fmt.Errorf("当前数据源（%s）暂不支持通过此入口新建模式", dbType)
+	}
+
+	return fmt.Sprintf("CREATE SCHEMA %s", quoteIdentByType(dbType, schemaName)), nil
+}
+
+func (a *App) CreateSchema(config connection.ConnectionConfig, dbName string, schemaName string) connection.QueryResult {
+	dbType := resolveDDLDBType(config)
+	targetDbName := strings.TrimSpace(dbName)
+	if targetDbName == "" {
+		targetDbName = strings.TrimSpace(config.Database)
+	}
+	if targetDbName == "" {
+		return connection.QueryResult{Success: false, Message: "目标数据库不能为空"}
+	}
+
+	query, err := buildCreateSchemaSQL(dbType, schemaName)
+	if err != nil {
+		return connection.QueryResult{Success: false, Message: err.Error()}
+	}
+
+	runConfig := buildRunConfigForDDL(config, dbType, targetDbName)
+	dbInst, err := a.getDatabase(runConfig)
+	if err != nil {
+		return connection.QueryResult{Success: false, Message: err.Error()}
+	}
+
+	if _, err := dbInst.Exec(query); err != nil {
+		return connection.QueryResult{Success: false, Message: err.Error()}
+	}
+
+	return connection.QueryResult{Success: true, Message: "模式创建成功"}
+}
+
 func resolveDDLDBType(config connection.ConnectionConfig) string {
 	dbType := strings.ToLower(strings.TrimSpace(config.Type))
 	if dbType == "doris" {

internal/app/methods_db_create_test.go

@@ -115,3 +115,58 @@ func TestCreateDatabase_SQLServerUsesBracketIdentifiers(t *testing.T) {
 		t.Fatalf("unexpected SQL Server create database SQL, want %q got %q", want, fakeDB.execQueries[0])
 	}
 }
+
+func TestBuildCreateSchemaSQL_PostgresQuotesSchemaName(t *testing.T) {
+	got, err := buildCreateSchemaSQL("postgresql", `sales"Ops`)
+	if err != nil {
+		t.Fatalf("expected postgres create schema SQL, got error: %v", err)
+	}
+	const want = `CREATE SCHEMA "sales""Ops"`
+	if got != want {
+		t.Fatalf("unexpected create schema SQL, want %q got %q", want, got)
+	}
+}
+
+func TestBuildCreateSchemaSQL_RejectsUnsupportedDatabaseType(t *testing.T) {
+	if _, err := buildCreateSchemaSQL("mysql", "sales"); err == nil {
+		t.Fatalf("expected unsupported database type error")
+	}
+}
+
+func TestCreateSchema_CustomPostgresUsesSelectedDatabase(t *testing.T) {
+	originalNewDatabaseFunc := newDatabaseFunc
+	originalResolveDialConfigWithProxyFunc := resolveDialConfigWithProxyFunc
+	t.Cleanup(func() {
+		newDatabaseFunc = originalNewDatabaseFunc
+		resolveDialConfigWithProxyFunc = originalResolveDialConfigWithProxyFunc
+	})
+
+	fakeDB := &fakeCreateDatabaseDB{}
+	newDatabaseFunc = func(dbType string) (db.Database, error) {
+		return fakeDB, nil
+	}
+	resolveDialConfigWithProxyFunc = func(raw connection.ConnectionConfig) (connection.ConnectionConfig, error) {
+		return raw, nil
+	}
+
+	app := NewAppWithSecretStore(secretstore.NewUnavailableStore("test"))
+	result := app.CreateSchema(connection.ConnectionConfig{
+		Type:     "custom",
+		Driver:   "pgx",
+		Database: "postgres",
+	}, "tenant_db", `tenant"schema`)
+
+	if !result.Success {
+		t.Fatalf("expected create schema success, got failure: %s", result.Message)
+	}
+	if fakeDB.connectConfig.Database != "tenant_db" {
+		t.Fatalf("expected create schema connection to use selected database tenant_db, got %q", fakeDB.connectConfig.Database)
+	}
+	if len(fakeDB.execQueries) != 1 {
+		t.Fatalf("expected one create schema statement, got %d: %#v", len(fakeDB.execQueries), fakeDB.execQueries)
+	}
+	const want = `CREATE SCHEMA "tenant""schema"`
+	if fakeDB.execQueries[0] != want {
+		t.Fatalf("unexpected create schema SQL, want %q got %q", want, fakeDB.execQueries[0])
+	}
+}