feat: 配置 golangci-lint 静态分析并修复存量违规

- 新增 backend/.golangci.yml 配置 12 个 linter（forbidigo、errorlint、errcheck、staticcheck、revive、gocritic、gosec、bodyclose、noctx、nilerr、goimports、gocyclo）
- 新增 lefthook.yml 配置 pre-commit hook 自动运行 lint
- 修复存量代码违规：errors.Is/As 替换、zap.Error 替换、import 排序、errcheck 修复
- 更新 README 补充编码规范说明
- 归档 backend-code-lint 变更

backend/cmd/desktop/main.go

@@ -13,10 +13,7 @@ import (
 	"strings"
 	"time"
 
-	"github.com/getlantern/systray"
-	"github.com/gin-gonic/gin"
-	"github.com/gofrs/flock"
-	"go.uber.org/zap"
+	"nex/embedfs"
 
 	"nex/backend/internal/config"
 	"nex/backend/internal/conversion"
@@ -28,9 +25,13 @@ import (
 	"nex/backend/internal/provider"
 	"nex/backend/internal/repository"
 	"nex/backend/internal/service"
-	pkgLogger "nex/backend/pkg/logger"
 
-	"nex/embedfs"
+	"github.com/getlantern/systray"
+	"github.com/gin-gonic/gin"
+	"github.com/gofrs/flock"
+	"go.uber.org/zap"
+
+	pkgLogger "nex/backend/pkg/logger"
 )
 
 var (
@@ -51,12 +52,16 @@ func main() {
 		showError("Nex Gateway", "已有 Nex 实例运行")
 		os.Exit(1)
 	}
-	defer singleLock.Unlock()
+	defer func() {
+		if err := singleLock.Unlock(); err != nil {
+			minimalLogger.Warn("释放实例锁失败", zap.Error(err))
+		}
+	}()
 
 	if err := checkPortAvailable(port); err != nil {
 		minimalLogger.Error("端口不可用", zap.Error(err))
 		showError("Nex Gateway", err.Error())
-		os.Exit(1)
+		return
 	}
 
 	cfg, err := config.LoadConfig()
@@ -75,7 +80,11 @@ func main() {
 	if err != nil {
 		minimalLogger.Fatal("初始化日志失败", zap.Error(err))
 	}
-	defer zapLogger.Sync()
+	defer func() {
+		if err := zapLogger.Sync(); err != nil {
+			minimalLogger.Warn("同步日志失败", zap.Error(err))
+		}
+	}()
 
 	cfg.PrintSummary(zapLogger)
 
@@ -144,14 +153,14 @@ func main() {
 	go func() {
 		zapLogger.Info("AI Gateway 启动", zap.String("addr", server.Addr))
 		if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
-			zapLogger.Fatal("服务器启动失败", zap.String("error", err.Error()))
+			zapLogger.Fatal("服务器启动失败", zap.Error(err))
 		}
 	}()
 
 	go func() {
 		time.Sleep(500 * time.Millisecond)
 		if err := openBrowser(fmt.Sprintf("http://localhost:%d", port)); err != nil {
-			zapLogger.Warn("无法打开浏览器", zap.String("error", err.Error()))
+			zapLogger.Warn("无法打开浏览器", zap.Error(err))
 		}
 	}()
 
@@ -193,7 +202,7 @@ func setupRoutes(r *gin.Engine, proxyHandler *handler.ProxyHandler, providerHand
 func setupStaticFiles(r *gin.Engine) {
 	distFS, err := fs.Sub(embedfs.FrontendDist, "frontend-dist")
 	if err != nil {
-		zapLogger.Fatal("无法加载前端资源", zap.String("error", err.Error()))
+		zapLogger.Fatal("无法加载前端资源", zap.Error(err))
 	}
 
 	getContentType := func(path string) string {
@@ -266,7 +275,7 @@ func setupSystray(port int) {
 			icon, err = embedfs.Assets.ReadFile("assets/icon.png")
 		}
 		if err != nil {
-			zapLogger.Error("无法加载托盘图标", zap.String("error", err.Error()))
+			zapLogger.Error("无法加载托盘图标", zap.Error(err))
 		}
 		systray.SetIcon(icon)
 		systray.SetTitle("Nex Gateway")
@@ -287,7 +296,9 @@ func setupSystray(port int) {
 			for {
 				select {
 				case <-mOpen.ClickedCh:
-					openBrowser(fmt.Sprintf("http://localhost:%d", port))
+					if err := openBrowser(fmt.Sprintf("http://localhost:%d", port)); err != nil {
+						zapLogger.Warn("打开浏览器失败", zap.Error(err))
+					}
 				case <-mAbout.ClickedCh:
 					showAbout()
 				case <-mQuit.ClickedCh:
@@ -308,7 +319,9 @@ func doShutdown() {
 	if server != nil {
 		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 		defer cancel()
-		server.Shutdown(ctx)
+		if err := server.Shutdown(ctx); err != nil && zapLogger != nil {
+			zapLogger.Warn("关闭服务器失败", zap.Error(err))
+		}
 	}
 
 	if shutdownCancel != nil {
@@ -346,8 +359,8 @@ func (s *SingletonLock) Lock() error {
 	return nil
 }
 
-func (s *SingletonLock) Unlock() {
-	s.flock.Unlock()
+func (s *SingletonLock) Unlock() error {
+	return s.flock.Unlock()
 }
 
 func openBrowser(url string) error {