Makefile: build with CGO_ENABLED=0; drop committed mcproxyctl binary

The binary was a build output checked in by mistake; ignore it.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Makefile

@@ -3,12 +3,13 @@
 MCR     := mcr.svc.mcp.metacircular.net:8443
 VERSION := $(shell git describe --tags --always --dirty)
 LDFLAGS := -trimpath -ldflags="-s -w -X main.version=$(VERSION)"
+CGO     := CGO_ENABLED=0
 
 mc-proxy:
-	go build $(LDFLAGS) -o mc-proxy ./cmd/mc-proxy
+	$(CGO) go build $(LDFLAGS) -o mc-proxy ./cmd/mc-proxy
 
 mcproxyctl:
-	go build -trimpath -ldflags="-s -w" -o mcproxyctl ./cmd/mcproxyctl
+	$(CGO) go build -trimpath -ldflags="-s -w" -o mcproxyctl ./cmd/mcproxyctl
 
 build:
 	go build ./...