fix(lint): 修复 handler 和 http2 模块 lint 错误

- 添加 nolint:errcheck 注释到 defer Close 调用
- 修复 websocket.go 中重复的 nolint 注释格式
- 添加 staticcheck SA1019 nolint 注释到 deprecated WriteScheduler
- 移除 sendfile_linux.go 中未使用的 platformLinux 常量
- 添加文件末尾换行符

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/handler/sendfile.go

@@ -125,4 +125,4 @@ func platformSendfile(conn net.Conn, file *os.File, offset, length int64) error
 	// macOS sendfile 签名复杂，简化使用 fallback
 	// Windows TransmitFile 需要特殊 API
 	return syscall.ENOTSUP
-}
+}

internal/handler/sendfile_linux.go

@@ -22,9 +22,6 @@ const (
 	MinSendfileSize = 8 * 1024
 )
 
-// platformLinux Linux 平台标识符。
-const platformLinux = "linux"
-
 // SendFile 零拷贝文件传输。
 //
 // 大文件使用系统调用直接从文件传输到 socket，避免用户空间拷贝，
@@ -120,16 +117,16 @@ func getSocketFd(conn net.Conn) (uintptr, error) {
 		if err != nil {
 			return 0, err
 		}
-		defer func() { _ = file.Close() }()
+		defer func() { _ = file.Close() }() //nolint:errcheck
 		return file.Fd(), nil
 	case *net.UnixConn:
 		file, err := c.File()
 		if err != nil {
 			return 0, err
 		}
-		defer func() { _ = file.Close() }()
+		defer func() { _ = file.Close() }() //nolint:errcheck
 		return file.Fd(), nil
 	default:
 		return 0, syscall.ENOTSUP
 	}
-}
+}

internal/handler/sendfile_other_test.go

@@ -245,4 +245,4 @@ func TestCopyFile_Error(t *testing.T) {
 	if err == nil {
 		t.Error("Expected error for offset beyond file size")
 	}
-}
+}

internal/handler/sendfile_test.go

@@ -277,4 +277,4 @@ func TestLinuxSendfile_NilConn(t *testing.T) {
 	if err == nil {
 		t.Error("Expected error for nil connection")
 	}
-}
+}

internal/http2/server.go

@@ -101,8 +101,9 @@ func NewServer(cfg *config.HTTP2Config, handler fasthttp.RequestHandler, tlsConf
 		MaxConcurrentStreams: uint32(maxConcurrentStreams),
 		IdleTimeout:          idleTimeout,
 		MaxReadFrameSize:     uint32(maxHeaderListSize),
-		NewWriteScheduler:    func() http2.WriteScheduler { return http2.NewPriorityWriteScheduler(nil) },
-		CountError:           func(_ string) {},
+		//nolint:staticcheck // SA1019: NewWriteScheduler deprecated
+		NewWriteScheduler: func() http2.WriteScheduler { return http2.NewPriorityWriteScheduler(nil) },
+		CountError:        func(_ string) {},
 	}
 
 	return &Server{

internal/proxy/websocket.go

@@ -227,11 +227,11 @@ func dialTarget(targetURL string, timeout time.Duration) (net.Conn, error) {
 			ServerName:         strings.Split(addr, ":")[0],
 		})
 		if err := tlsConn.SetDeadline(time.Now().Add(timeout)); err != nil {
-			_ = conn.Close() //nolint:errcheck //nolint:errcheck
+			_ = conn.Close() //nolint:errcheck // 错误处理中关闭连接
 			return nil, fmt.Errorf("failed to set TLS deadline: %w", err)
 		}
 		if err := tlsConn.Handshake(); err != nil {
-			_ = conn.Close() //nolint:errcheck //nolint:errcheck
+			_ = conn.Close() //nolint:errcheck // 错误处理中关闭连接
 			return nil, fmt.Errorf("TLS handshake failed: %w", err)
 		}
 		return tlsConn, nil
@@ -396,14 +396,14 @@ func WebSocket(ctx *fasthttp.RequestCtx, target *loadbalance.Target, timeout tim
 	// 步骤5: 检查响应状态码（期望 101 Switching Protocols）
 	if resp.StatusCode != http.StatusSwitchingProtocols {
 		// 关闭响应 body（升级失败时）
-		_ = resp.Body.Close() //nolint:errcheck //nolint:errcheck
+		_ = resp.Body.Close() //nolint:errcheck // 错误处理中关闭响应体
 		return fmt.Errorf("backend rejected WebSocket upgrade: %s", resp.Status)
 	}
 
 	// 步骤6: 将升级响应发送回客户端
 	if err := writeUpgradeResponse(clientConn, resp); err != nil {
 		// 关闭响应 body（写入失败时）
-		_ = resp.Body.Close() //nolint:errcheck //nolint:errcheck
+		_ = resp.Body.Close() //nolint:errcheck // 错误处理中关闭响应体
 		return fmt.Errorf("failed to send upgrade response to client: %w", err)
 	}