build: add Makefile with help/install/run/test/clean targets

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Makefile

@@ -0,0 +1,25 @@
+# Pipeline Network Diagram Editor
+
+PYTHON ?= python3
+PIP ?= $(PYTHON) -m pip
+
+.DEFAULT_GOAL := help
+
+.PHONY: help install run test lint clean
+
+help: ## Show this help
+	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | \
+		awk 'BEGIN {FS = ":.*?## "}; {printf "  \033[36m%-12s\033[0m %s\n", $$1, $$2}'
+
+install: ## Install runtime and test dependencies
+	$(PIP) install -r requirements.txt
+
+run: ## Launch the editor
+	$(PYTHON) -m pipeline_editor
+
+test: ## Run the test suite headless
+	QT_QPA_PLATFORM=offscreen $(PYTHON) -m pytest
+
+clean: ## Remove Python caches and build artifacts
+	rm -rf build dist *.egg-info .pytest_cache .coverage htmlcov
+	find . -type d -name __pycache__ -prune -exec rm -rf {} +