[misc] Move shared components to shared directory (#4286)

Moved the following directories:

```
  - management/client → shared/management/client
  - management/domain → shared/management/domain
  - management/proto → shared/management/proto
  - signal/client → shared/signal/client
  - signal/proto → shared/signal/proto
  - relay/client → shared/relay/client
  - relay/auth → shared/relay/auth
```

and adjusted import paths

shared/relay/client/dialer/quic/conn.go

@@ -0,0 +1,97 @@
+package quic
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+	"time"
+
+	"github.com/quic-go/quic-go"
+	log "github.com/sirupsen/logrus"
+
+	netErr "github.com/netbirdio/netbird/shared/relay/client/dialer/net"
+)
+
+const (
+	Network = "quic"
+)
+
+type Addr struct {
+	addr string
+}
+
+func (a Addr) Network() string {
+	return Network
+}
+
+func (a Addr) String() string {
+	return a.addr
+}
+
+type Conn struct {
+	session quic.Connection
+	ctx     context.Context
+}
+
+func NewConn(session quic.Connection) net.Conn {
+	return &Conn{
+		session: session,
+		ctx:     context.Background(),
+	}
+}
+
+func (c *Conn) Read(b []byte) (n int, err error) {
+	dgram, err := c.session.ReceiveDatagram(c.ctx)
+	if err != nil {
+		return 0, c.remoteCloseErrHandling(err)
+	}
+
+	n = copy(b, dgram)
+	return n, nil
+}
+
+func (c *Conn) Write(b []byte) (int, error) {
+	err := c.session.SendDatagram(b)
+	if err != nil {
+		err = c.remoteCloseErrHandling(err)
+		log.Errorf("failed to write to QUIC stream: %v", err)
+		return 0, err
+	}
+	return len(b), nil
+}
+
+func (c *Conn) RemoteAddr() net.Addr {
+	return c.session.RemoteAddr()
+}
+
+func (c *Conn) LocalAddr() net.Addr {
+	if c.session != nil {
+		return c.session.LocalAddr()
+	}
+	return Addr{addr: "unknown"}
+}
+
+func (c *Conn) SetReadDeadline(t time.Time) error {
+	return fmt.Errorf("SetReadDeadline is not implemented")
+}
+
+func (c *Conn) SetWriteDeadline(t time.Time) error {
+	return fmt.Errorf("SetWriteDeadline is not implemented")
+}
+
+func (c *Conn) SetDeadline(t time.Time) error {
+	return nil
+}
+
+func (c *Conn) Close() error {
+	return c.session.CloseWithError(0, "normal closure")
+}
+
+func (c *Conn) remoteCloseErrHandling(err error) error {
+	var appErr *quic.ApplicationError
+	if errors.As(err, &appErr) && appErr.ErrorCode == 0x0 {
+		return netErr.ErrClosedByServer
+	}
+	return err
+}

shared/relay/client/dialer/quic/quic.go

@@ -0,0 +1,99 @@
+package quic
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+	"strings"
+	"time"
+
+	"github.com/quic-go/quic-go"
+	log "github.com/sirupsen/logrus"
+
+	quictls "github.com/netbirdio/netbird/relay/tls"
+	nbnet "github.com/netbirdio/netbird/util/net"
+)
+
+type Dialer struct {
+}
+
+func (d Dialer) Protocol() string {
+	return Network
+}
+
+func (d Dialer) Dial(ctx context.Context, address string) (net.Conn, error) {
+	quicURL, err := prepareURL(address)
+	if err != nil {
+		return nil, err
+	}
+
+	// Get the base TLS config
+	tlsClientConfig := quictls.ClientQUICTLSConfig()
+
+	// Set ServerName to hostname if not an IP address
+	host, _, splitErr := net.SplitHostPort(quicURL)
+	if splitErr == nil && net.ParseIP(host) == nil {
+		// It's a hostname, not an IP - modify directly
+		tlsClientConfig.ServerName = host
+	}
+
+	quicConfig := &quic.Config{
+		KeepAlivePeriod:   30 * time.Second,
+		MaxIdleTimeout:    4 * time.Minute,
+		EnableDatagrams:   true,
+		InitialPacketSize: 1452,
+	}
+
+	udpConn, err := nbnet.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
+	if err != nil {
+		log.Errorf("failed to listen on UDP: %s", err)
+		return nil, err
+	}
+
+	udpAddr, err := net.ResolveUDPAddr("udp", quicURL)
+	if err != nil {
+		log.Errorf("failed to resolve UDP address: %s", err)
+		return nil, err
+	}
+
+	session, err := quic.Dial(ctx, udpConn, udpAddr, tlsClientConfig, quicConfig)
+	if err != nil {
+		if errors.Is(err, context.Canceled) {
+			return nil, err
+		}
+		log.Errorf("failed to dial to Relay server via QUIC '%s': %s", quicURL, err)
+		return nil, err
+	}
+
+	conn := NewConn(session)
+	return conn, nil
+}
+
+func prepareURL(address string) (string, error) {
+	var host string
+	var defaultPort string
+
+	switch {
+	case strings.HasPrefix(address, "rels://"):
+		host = address[7:]
+		defaultPort = "443"
+	case strings.HasPrefix(address, "rel://"):
+		host = address[6:]
+		defaultPort = "80"
+	default:
+		return "", fmt.Errorf("unsupported scheme: %s", address)
+	}
+
+	finalHost, finalPort, err := net.SplitHostPort(host)
+	if err != nil {
+		if strings.Contains(err.Error(), "missing port") {
+			return host + ":" + defaultPort, nil
+		}
+
+		// return any other split error as is
+		return "", err
+	}
+
+	return finalHost + ":" + finalPort, nil
+}