chore: LICENSE, CI workflow, gitignore hygiene, makefile targets

Makefile

@@ -1,4 +1,4 @@
-.PHONY: build test lint clean install
+.PHONY: build test lint test-race cover tidy clean install
 
 BIN := harness-sync
 VERSION ?= $(shell git describe --tags --always --dirty 2>/dev/null || echo dev)
@@ -11,7 +11,19 @@ test:
 	go test ./...
 
 lint:
-	go vet ./...
+	golangci-lint run ./...
+
+test-race:
+	go test -race -count=1 ./...
+
+cover:
+	go test -coverprofile=coverage.out ./...
+	go tool cover -html=coverage.out -o coverage.html
+	@echo "open coverage.html"
+
+tidy:
+	go mod tidy
+	gofmt -s -w .
 
 install: build
 	install -m 0755 $(BIN) $$HOME/.local/bin/$(BIN)