fix(darwin): use scutil for provisioning hostname (#485)

macOS Sequoia with Private Wi-Fi Address enabled causes os.Hostname()
to return generic names like "Mac.lan" from DHCP instead of the real
computer name. The /utility provisioning endpoint sends this raw,
resulting in devices named "Mac-lan" in the dashboard.

Fallback chain: ComputerName → LocalHostName → os.Hostname()

LocalHostName can also be affected by DHCP. ComputerName is the
user-set display name from System Settings, fully immune to network state.

internal/controld/config.go

@@ -10,7 +10,6 @@ import (
 	"io"
 	"net"
 	"net/http"
-	"os"
 	"runtime"
 	"strings"
 	"time"
@@ -127,7 +126,7 @@ func FetchResolverUID(ctx context.Context, req *UtilityOrgRequest, version strin
 
 	hostname := req.Hostname
 	if req.Hostname == "" {
-		hostname, _ = os.Hostname()
+		hostname, _ = preferredHostname()
 		ctrld.Log(ctx, logger.Debug(), "Using system hostname: %s", hostname)
 		req.Hostname = hostname
 	} else {