Add VERSION variable and push target to Makefile

Extract VERSION variable (was inline). Add version tag to docker image.
Add push target that builds then pushes to MCR.

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

Makefile

@@ -1,6 +1,8 @@
-.PHONY: build test vet lint proto proto-lint clean docker all devserver
+.PHONY: build test vet lint proto proto-lint clean docker push all devserver
 
-LDFLAGS := -trimpath -ldflags="-s -w -X main.version=$(shell git describe --tags --always --dirty)"
+MCR     := mcr.svc.mcp.metacircular.net:8443
+VERSION := $(shell git describe --tags --always --dirty)
+LDFLAGS := -trimpath -ldflags="-s -w -X main.version=$(VERSION)"
 
 mc-proxy:
 	go build $(LDFLAGS) -o mc-proxy ./cmd/mc-proxy
@@ -33,7 +35,10 @@ clean:
 	rm -f mc-proxy mcproxyctl
 
 docker:
-	docker build --build-arg VERSION=$(shell git describe --tags --always --dirty) -t mc-proxy -f Dockerfile .
+	docker build --build-arg VERSION=$(VERSION) -t $(MCR)/mc-proxy:$(VERSION) -f Dockerfile .
+
+push: docker
+	docker push $(MCR)/mc-proxy:$(VERSION)
 
 devserver: mc-proxy
 	@mkdir -p srv