Add mcproxyctl CLI for gRPC admin API

Introduces a new command-line tool for managing mc-proxy via the gRPC
admin API over Unix socket. Commands include route and firewall rule
CRUD operations, health checks, and status queries.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Makefile

@@ -5,6 +5,9 @@ LDFLAGS := -trimpath -ldflags="-s -w -X main.version=$(shell git describe --tags
 mc-proxy:
 	go build $(LDFLAGS) -o mc-proxy ./cmd/mc-proxy
 
+mcproxyctl:
+	go build -trimpath -ldflags="-s -w" -o mcproxyctl ./cmd/mcproxyctl
+
 build:
 	go build ./...
 
@@ -27,7 +30,7 @@ proto-lint:
 	buf breaking --against '.git#branch=master,subdir=proto'
 
 clean:
-	rm -f mc-proxy
+	rm -f mc-proxy mcproxyctl
 
 docker:
 	docker build --build-arg VERSION=$(shell git describe --tags --always --dirty) -t mc-proxy -f Dockerfile .