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/golang.org/x/term/README.md

@@ -0,0 +1,16 @@
+# Go terminal/console support
+
+[![Go Reference](https://pkg.go.dev/badge/golang.org/x/term.svg)](https://pkg.go.dev/golang.org/x/term)
+
+This repository provides Go terminal and console support packages.
+
+## Report Issues / Send Patches
+
+This repository uses Gerrit for code changes. To learn how to submit changes to
+this repository, see https://go.dev/doc/contribute.
+
+The git repository is https://go.googlesource.com/term.
+
+The main issue tracker for the term repository is located at
+https://go.dev/issues. Prefix your issue with "x/term:" in the
+subject line, so it is easy to find.