Add Nix flake for mcrctl

Vendor dependencies and expose mcrctl binary via nix build.

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

vendor/github.com/go-chi/chi/v5/Makefile

@@ -0,0 +1,22 @@
+.PHONY: all
+all:
+	@echo "**********************************************************"
+	@echo "**                    chi build tool                    **"
+	@echo "**********************************************************"
+
+
+.PHONY: test
+test:
+	go clean -testcache && $(MAKE) test-router && $(MAKE) test-middleware
+
+.PHONY: test-router
+test-router:
+	go test -race -v .
+
+.PHONY: test-middleware
+test-middleware:
+	go test -race -v ./middleware
+
+.PHONY: docs
+docs:
+	npx docsify-cli serve ./docs