feat: initialize Go agent module with config, Makefile and project structure

Agent/Makefile

@@ -0,0 +1,17 @@
+.PHONY: build build-windows build-linux clean
+
+BINARY=nexus-agent
+VERSION=$(shell git describe --tags --always --dirty 2>/dev/null || echo "dev")
+LDFLAGS=-ldflags "-s -w -X main.version=$(VERSION)"
+
+build:
+	go build $(LDFLAGS) -o bin/$(BINARY) ./cmd/agent
+
+build-windows:
+	GOOS=windows GOARCH=amd64 go build $(LDFLAGS) -o bin/$(BINARY).exe ./cmd/agent
+
+build-linux:
+	GOOS=linux GOARCH=amd64 go build $(LDFLAGS) -o bin/$(BINARY)-linux ./cmd/agent
+
+clean:
+	rm -rf bin/