fix: 桌面应用跨平台编译和单实例锁

- 使用 gofrs/flock 替代 syscall.Flock 以支持 Windows
- 引入 SingletonLock 结构体，支持锁路径参数化（测试与生产隔离）
- 对齐服务初始化流程与 cmd/server（RoutingCache、StatsBuffer）
- 添加 gofrs/flock 依赖
- 重写单例测试，覆盖加锁/解锁/重复加锁场景
- 更新 desktop-app 规范，补充跨平台锁细节
- 新增 cross-platform-singleton 规范

backend/cmd/desktop/main.go

@@ -12,11 +12,11 @@ import (
 	"path/filepath"
 	"runtime"
 	"strings"
-	"syscall"
 	"time"
 
 	"github.com/gin-gonic/gin"
 	"github.com/getlantern/systray"
+	"github.com/gofrs/flock"
 	"github.com/pressly/goose/v3"
 	"go.uber.org/zap"
 	"gorm.io/driver/sqlite"
@@ -47,11 +47,12 @@ var (
 func main() {
 	port := 9826
 
-	if err := acquireSingleInstance(); err != nil {
+	singleLock := NewSingletonLock(filepath.Join(os.TempDir(), "nex-gateway.lock"))
+	if err := singleLock.Lock(); err != nil {
 		showError("Nex Gateway", "已有 Nex 实例运行")
 		os.Exit(1)
 	}
-	defer releaseSingleInstance()
+	defer singleLock.Unlock()
 
 	if err := checkPortAvailable(port); err != nil {
 		showError("Nex Gateway", err.Error())
@@ -89,10 +90,21 @@ func main() {
 	modelRepo := repository.NewModelRepository(db)
 	statsRepo := repository.NewStatsRepository(db)
 
-	providerService := service.NewProviderService(providerRepo, modelRepo)
-	modelService := service.NewModelService(modelRepo, providerRepo)
-	routingService := service.NewRoutingService(modelRepo, providerRepo)
-	statsService := service.NewStatsService(statsRepo)
+	routingCache := service.NewRoutingCache(modelRepo, providerRepo, zapLogger)
+	if err := routingCache.Preload(); err != nil {
+		zapLogger.Warn("缓存预热失败，将使用懒加载", zap.Error(err))
+	}
+
+	statsBuffer := service.NewStatsBuffer(statsRepo, zapLogger,
+		service.WithFlushInterval(5*time.Second),
+		service.WithFlushThreshold(100))
+	statsBuffer.Start()
+	defer statsBuffer.Stop()
+
+	providerService := service.NewProviderService(providerRepo, modelRepo, routingCache)
+	modelService := service.NewModelService(modelRepo, providerRepo, routingCache)
+	routingService := service.NewRoutingService(routingCache)
+	statsService := service.NewStatsService(statsRepo, statsBuffer)
 
 	registry := conversion.NewMemoryRegistry()
 	if err := registry.Register(openai.NewAdapter()); err != nil {
@@ -378,31 +390,29 @@ func checkPortAvailable(port int) error {
 	return nil
 }
 
-var lockFile *os.File
+type SingletonLock struct {
+	flock *flock.Flock
+}
 
-func acquireSingleInstance() error {
-	lockPath := filepath.Join(os.TempDir(), "nex-gateway.lock")
+func NewSingletonLock(lockPath string) *SingletonLock {
+	return &SingletonLock{
+		flock: flock.New(lockPath),
+	}
+}
 
-	f, err := os.OpenFile(lockPath, os.O_CREATE|os.O_RDWR, 0666)
+func (s *SingletonLock) Lock() error {
+	locked, err := s.flock.TryLock()
 	if err != nil {
 		return err
 	}
-
-	err = syscall.Flock(int(f.Fd()), syscall.LOCK_EX|syscall.LOCK_NB)
-	if err != nil {
-		f.Close()
+	if !locked {
 		return fmt.Errorf("已有实例运行")
 	}
-
-	lockFile = f
 	return nil
 }
 
-func releaseSingleInstance() {
-	if lockFile != nil {
-		syscall.Flock(int(lockFile.Fd()), syscall.LOCK_UN)
-		lockFile.Close()
-	}
+func (s *SingletonLock) Unlock() {
+	s.flock.Unlock()
 }
 
 func openBrowser(url string) error {