test(handlers): use deterministic IP in BMX registry test

soundtouch.local relied on mDNS resolution, which works on developer
macOS but not in CI/Linux. With the new server_url validation, an
unresolvable hostname now correctly causes DNS to refuse to start --
which flips dnsEnabled to false and made the test fail honestly instead
of passing while DNS was silently broken. Switch the fixture to
127.0.0.1 so the test exercises the DNS-enabled path everywhere.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

pkg/service/handlers/bmx_registry_test.go

@@ -21,7 +21,7 @@ func TestHandleBMXRegistry_DNSDependent(t *testing.T) {
 	ds := datastore.NewDataStore(tempDir)
 	_ = ds.Initialize()
 
-	localURL := "https://soundtouch.local"
+	localURL := "https://127.0.0.1"
 	server := NewServer(ds, nil, localURL, false, false, false)
 
 	t.Run("DNSEnabled_UsesBoseURL", func(t *testing.T) {