build: add Makefile wrapping npm/tauri tasks

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

Makefile

@@ -0,0 +1,43 @@
+# Pipeline Diagram Editor — common developer tasks.
+# Run `make help` to list targets.
+
+.DEFAULT_GOAL := help
+.PHONY: help install dev build preview test test-watch typecheck \
+        tauri-dev tauri-build tauri-build-debug clean
+
+help: ## Show this help
+	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) \
+		| awk 'BEGIN {FS = ":.*?## "}; {printf "  \033[36m%-18s\033[0m %s\n", $$1, $$2}'
+
+install: ## Install npm dependencies
+	npm install
+
+dev: ## Start the Vite dev server
+	npm run dev
+
+build: ## Type-check and build the web bundle
+	npm run build
+
+preview: ## Preview the production build
+	npm run preview
+
+test: ## Run the test suite once
+	npm run test
+
+test-watch: ## Run tests in watch mode
+	npm run test:watch
+
+typecheck: ## Type-check without emitting
+	npx tsc -b
+
+tauri-dev: ## Run the Tauri app in development
+	npm run tauri:dev
+
+tauri-build: ## Build the Tauri desktop app
+	npm run tauri:build
+
+tauri-build-debug: ## Build the Tauri desktop app (debug)
+	npm run tauri:build:debug
+
+clean: ## Remove build artifacts
+	rm -rf dist .vite src-tauri/target