Add TURN relay support for daemon mode

-turn-url and -turn-secret flags on the daemon; credentials generated
using coturn use-auth-secret HMAC-SHA1 scheme (same as browser mode).
ICEServers field on mesh.Mesh threads extra ICE servers through to
every PeerConnection created by the anchor client.

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

internal/netmgr/manager.go

@@ -6,13 +6,20 @@ package netmgr
 
 import (
 	"context"
+	"crypto/hmac"
+	"crypto/sha1"
 	"crypto/sha256"
+	"encoding/base64"
 	"encoding/hex"
 	"fmt"
 	"log"
 	"os"
 	"path/filepath"
+	"strconv"
 	"sync"
+	"time"
+
+	"github.com/pion/webrtc/v3"
 
 	"github.com/waste-go/internal/anchor"
 	"github.com/waste-go/internal/crypto"
@@ -28,6 +35,8 @@ type Config struct {
 	StoreDir       string // base directory for per-network SQLite files
 	AnchorURL      string // WebSocket anchor URL used for all networks
 	ShareDir       string // default share directory; overridden per network via Join or SetShareDir
+	TurnURL        string // optional TURN server URL, e.g. "turn:your-vps:3478"
+	TurnSecret     string // shared secret for coturn use-auth-secret HMAC credential
 }
 
 // Network is a single joined network context.
@@ -113,6 +122,9 @@ func (mgr *Manager) Join(name, shareDir string) (string, error) {
 	m.DownloadDir = filepath.Join(mgr.cfg.StoreDir, "downloads-"+netID_full)
 	capturedNetID := netID
 	m.ScanFiles = func() []proto.FileEntry { return mgr.ScanAllShares(capturedNetID) }
+	if ice := mgr.turnICEServers(); ice != nil {
+		m.ICEServers = ice
+	}
 
 	// Forward all mesh events to the Manager's fan-out, tagging with network_id.
 	meshEvents := m.Subscribe()
@@ -198,6 +210,9 @@ func (mgr *Manager) JoinByHash(netHash64, shareDir string) (string, error) {
 	m.DownloadDir = filepath.Join(mgr.cfg.StoreDir, "downloads-"+netID)
 	capturedNetID2 := netID
 	m.ScanFiles = func() []proto.FileEntry { return mgr.ScanAllShares(capturedNetID2) }
+	if ice := mgr.turnICEServers(); ice != nil {
+		m.ICEServers = ice
+	}
 
 	meshEvents := m.Subscribe()
 	go func() {
@@ -411,6 +426,26 @@ func (mgr *Manager) emit(msg proto.IpcMessage) {
 	}
 }
 
+// turnICEServers returns TURN ICE servers if TurnURL and TurnSecret are set,
+// using coturn's use-auth-secret HMAC-SHA1 time-limited credential scheme.
+// Returns nil if TURN is not configured.
+func (mgr *Manager) turnICEServers() []webrtc.ICEServer {
+	if mgr.cfg.TurnURL == "" || mgr.cfg.TurnSecret == "" {
+		return nil
+	}
+	// Username = Unix timestamp 1 hour from now.
+	expiry := strconv.FormatInt(time.Now().Add(time.Hour).Unix(), 10)
+	mac := hmac.New(sha1.New, []byte(mgr.cfg.TurnSecret))
+	mac.Write([]byte(expiry))
+	credential := base64.StdEncoding.EncodeToString(mac.Sum(nil))
+	return []webrtc.ICEServer{{
+		URLs:           []string{mgr.cfg.TurnURL},
+		Username:       expiry,
+		Credential:     credential,
+		CredentialType: webrtc.ICECredentialTypePassword,
+	}}
+}
+
 // ── helpers ───────────────────────────────────────────────────────────────────
 
 func hashNetName(name string) string {