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/golang-migrate/migrate/v4/CONTRIBUTING.md

@@ -0,0 +1,24 @@
+# Development, Testing and Contributing
+
+  1. Make sure you have a running Docker daemon
+     (Install for [MacOS](https://docs.docker.com/docker-for-mac/))
+  1. Use a version of Go that supports [modules](https://golang.org/cmd/go/#hdr-Modules__module_versions__and_more) (e.g. Go 1.11+)
+  1. Fork this repo and `git clone` somewhere to `$GOPATH/src/github.com/golang-migrate/migrate`
+      * Ensure that [Go modules are enabled](https://golang.org/cmd/go/#hdr-Preliminary_module_support) (e.g. your repo path or the `GO111MODULE` environment variable are set correctly)
+  1. Install [golangci-lint](https://github.com/golangci/golangci-lint#install)
+  1. Run the linter: `golangci-lint run`
+  1. Confirm tests are working: `make test-short`
+  1. Write awesome code ...
+  1. `make test` to run all tests against all database versions
+  1. Push code and open Pull Request
+ 
+Some more helpful commands:
+
+  * You can specify which database/ source tests to run:
+    `make test-short SOURCE='file go_bindata' DATABASE='postgres cassandra'`
+  * After `make test`, run `make html-coverage` which opens a shiny test coverage overview.
+  * `make build-cli` builds the CLI in directory `cli/build/`.
+  * `make list-external-deps` lists all external dependencies for each package
+  * `make docs && make open-docs` opens godoc in your browser, `make kill-docs` kills the godoc server.
+    Repeatedly call `make docs` to refresh the server.
+  * Set the `DOCKER_API_VERSION` environment variable to the latest supported version if you get errors regarding the docker client API version being too new.