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-viper/mapstructure/v2/reflect_go1_19.go

@@ -0,0 +1,44 @@
+//go:build !go1.20
+
+package mapstructure
+
+import "reflect"
+
+func isComparable(v reflect.Value) bool {
+	k := v.Kind()
+	switch k {
+	case reflect.Invalid:
+		return false
+
+	case reflect.Array:
+		switch v.Type().Elem().Kind() {
+		case reflect.Interface, reflect.Array, reflect.Struct:
+			for i := 0; i < v.Type().Len(); i++ {
+				// if !v.Index(i).Comparable() {
+				if !isComparable(v.Index(i)) {
+					return false
+				}
+			}
+			return true
+		}
+		return v.Type().Comparable()
+
+	case reflect.Interface:
+		// return v.Elem().Comparable()
+		return isComparable(v.Elem())
+
+	case reflect.Struct:
+		for i := 0; i < v.NumField(); i++ {
+			return false
+
+			// if !v.Field(i).Comparable() {
+			if !isComparable(v.Field(i)) {
+				return false
+			}
+		}
+		return true
+
+	default:
+		return v.Type().Comparable()
+	}
+}