fix: 修复后端配置加载测试失败

- 修复 viper SafeWriteConfig 与 SetConfigFile 不兼容问题
  - 将 SafeWriteConfig() 替换为 SafeWriteConfigAs(configPath)
  - 绕过 viper 的 configPaths 检查
- 调整 Makefile 测试命令分类
  - backend-test: 仅运行后端核心测试
  - backend-test-all: 运行全部后端测试（含 desktop）
  - desktop-test: 单独运行桌面应用测试
- 同步 config-management 和 test-coverage 规范

Makefile

@@ -1,11 +1,11 @@
 .PHONY: all dev build test lint clean \
-	backend-build backend-run backend-dev backend-test backend-test-unit backend-test-integration backend-test-coverage \
+	backend-build backend-run backend-dev backend-test backend-test-all backend-test-unit backend-test-integration backend-test-coverage \
 	backend-lint backend-clean backend-deps backend-generate \
 	backend-db-up backend-db-down backend-db-status backend-db-create \
 	test-mysql-up test-mysql-down test-mysql test-mysql-quick \
 	frontend-build frontend-dev frontend-test frontend-test-watch frontend-test-coverage frontend-test-e2e frontend-lint frontend-clean \
 	desktop-build desktop-build-mac desktop-build-win desktop-build-linux \
-	desktop-dev desktop-package-mac desktop-package-win desktop-package-linux desktop-clean \
+	desktop-dev desktop-test desktop-package-mac desktop-package-win desktop-package-linux desktop-clean \
 	desktop-prepare-frontend desktop-prepare-embedfs
 
 # ============================================
@@ -19,7 +19,7 @@ dev:
 build: backend-build frontend-build
 	@echo "✅ Build complete"
 
-test: backend-test frontend-test
+test: backend-test desktop-test frontend-test
 	@echo "✅ All tests passed"
 
 lint: backend-lint frontend-lint
@@ -41,6 +41,9 @@ backend-dev:
 	cd backend && go run ./cmd/server
 
 backend-test:
+	cd backend && go test ./internal/... ./pkg/... ./tests/... ./cmd/server/... -v
+
+backend-test-all:
 	cd backend && go test ./... -v
 
 backend-test-unit:
@@ -179,6 +182,9 @@ desktop-dev: desktop-prepare-frontend desktop-prepare-embedfs
 	@echo "🖥️  Starting desktop app in dev mode..."
 	cd backend && go run ./cmd/desktop
 
+desktop-test:
+	cd backend && go test ./cmd/desktop/... -v
+
 desktop-package-mac:
 	./scripts/build/package-macos.sh
 

backend/internal/config/config.go

@@ -231,7 +231,7 @@ func setupConfigFile(v *viper.Viper, configPath string) error {
 			return appErrors.Wrap(appErrors.ErrInternal, err)
 		}
 		// 配置文件不存在，创建默认配置文件
-		writeErr := v.SafeWriteConfig()
+		writeErr := v.SafeWriteConfigAs(configPath)
 		if writeErr == nil {
 			return nil
 		}

openspec/specs/config-management/spec.md

@@ -174,7 +174,7 @@
    3. 设置默认值
    4. 绑定 CLI 参数
    5. 绑定环境变量
-  6. 读取配置文件
+   6. 读取配置文件（不存在时自动创建）
    7. 反序列化到结构体
    8. 验证配置
    9. 打印配置摘要

openspec/specs/test-coverage/spec.md

@@ -31,16 +31,27 @@
 - **THEN** SHALL 测试请求转换、响应转换、流式转换
 - **THEN** SHALL 验证转换的准确性和完整性
 
-#### Scenario: config 加载管道集成测试
+#### Scenario: LoadConfigFromPath 默认值验证
 
 - **WHEN** 运行 config 加载管道的集成测试
 - **THEN** SHALL 验证 LoadConfigFromPath 正确加载默认值
-- **THEN** SHALL 验证环境变量（`NEX_` 前缀）覆盖默认值
 - **THEN** SHALL 验证 YAML 配置文件正确读取
 - **THEN** SHALL 验证优先级链：CLI 参数 > 环境变量 > YAML 文件 > 默认值
 - **THEN** SHALL 验证首次启动自动创建配置文件
 - **THEN** SHALL 验证 SaveConfig 后重新 LoadConfig 数据一致
 
+#### Scenario: 环境变量覆盖验证
+
+- **WHEN** 设置 `NEX_SERVER_PORT=9000` 和 `NEX_LOG_LEVEL=debug`
+- **THEN** SHALL 成功加载
+- **THEN** 配置值 SHALL 反映环境变量覆盖
+
+#### Scenario: 自动创建配置文件验证
+
+- **WHEN** 调用 `LoadConfigFromPath` 并指向不存在的文件路径
+- **THEN** SHALL 成功加载（不返回 `missing configuration for 'configPath'` 错误）
+- **THEN** SHALL 返回默认配置对象
+
 #### Scenario: handler 错误分支测试
 
 - **WHEN** 运行 handler 层的单元测试