Add Nix flake for mciasctl and mciasgrpcctl

Vendor dependencies and expose control program binaries via
nix build. Uses nixpkgs-unstable for Go 1.26 support.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/github.com/go-webauthn/webauthn/protocol/signals.go

@@ -0,0 +1,51 @@
+package protocol
+
+// NewSignalAllAcceptedCredentials creates a new SignalAllAcceptedCredentials struct that can simply be encoded with
+// json.Marshal.
+func NewSignalAllAcceptedCredentials(rpid string, user AllAcceptedCredentialsUser) *SignalAllAcceptedCredentials {
+	if user == nil {
+		return nil
+	}
+
+	credentials := user.WebAuthnCredentialIDs()
+
+	ids := make([]URLEncodedBase64, len(credentials))
+
+	for i, id := range credentials {
+		ids[i] = id
+	}
+
+	return &SignalAllAcceptedCredentials{
+		AllAcceptedCredentialIDs: ids,
+		RPID:                     rpid,
+		UserID:                   user.WebAuthnID(),
+	}
+}
+
+// SignalAllAcceptedCredentials is a struct which represents the CDDL of the same name.
+type SignalAllAcceptedCredentials struct {
+	AllAcceptedCredentialIDs []URLEncodedBase64 `json:"allAcceptedCredentialIds"`
+	RPID                     string             `json:"rpId"`
+	UserID                   URLEncodedBase64   `json:"userId"`
+}
+
+// SignalCurrentUserDetails is a struct which represents the CDDL of the same name.
+type SignalCurrentUserDetails struct {
+	DisplayName string           `json:"displayName"`
+	Name        string           `json:"name"`
+	RPID        string           `json:"rpId"`
+	UserID      URLEncodedBase64 `json:"userId"`
+}
+
+// SignalUnknownCredential is a struct which represents the CDDL of the same name.
+type SignalUnknownCredential struct {
+	CredentialID URLEncodedBase64 `json:"credentialId"`
+	RPID         string           `json:"rpId"`
+}
+
+// AllAcceptedCredentialsUser is an interface that can be implemented by a user to provide information about their
+// accepted credentials.
+type AllAcceptedCredentialsUser interface {
+	WebAuthnID() []byte
+	WebAuthnCredentialIDs() [][]byte
+}