add: comprehensive TDD test infrastructure

- Add Vitest + jsdom testing framework
- Create unit tests for engine.js and generator.js
- Add integration tests for end-to-end workflows
- Include test utilities and setup helpers
- Document testing approach in TESTING.md
- Document all dependencies in DEPENDS.md
- Add Makefile with test targets and dev workflow

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Makefile

@@ -0,0 +1,139 @@
+.PHONY: help install test test-watch test-coverage test-ui clean serve lint format deps-check deps-update
+
+# Default target
+help:
+	@echo "Timeline SVG Generator - Make Targets"
+	@echo "====================================="
+	@echo ""
+	@echo "Development:"
+	@echo "  install       Install development dependencies"
+	@echo "  serve         Start local development server"
+	@echo "  clean         Clean node_modules and coverage"
+	@echo ""
+	@echo "Testing:"
+	@echo "  test          Run all tests once"
+	@echo "  test-watch    Run tests in watch mode (TDD)"
+	@echo "  test-coverage Run tests with coverage report"
+	@echo "  test-ui       Open browser-based test UI"
+	@echo ""
+	@echo "Quality:"
+	@echo "  lint          Run code linting (if configured)"
+	@echo "  format        Format code (if configured)"
+	@echo ""
+	@echo "Dependencies:"
+	@echo "  deps-check    Check for outdated dependencies"
+	@echo "  deps-update   Update dependencies"
+	@echo "  deps-audit    Security audit of dependencies"
+	@echo ""
+
+# Development setup
+install:
+	@echo "Installing development dependencies..."
+	npm install
+	@echo "✅ Dependencies installed"
+
+# Testing targets
+test:
+	@echo "Running tests..."
+	@if [ ! -d "node_modules" ]; then \
+		echo "❌ Dependencies not installed. Run 'make install' first."; \
+		exit 1; \
+	fi
+	npm test
+
+test-watch:
+	@echo "Starting test watch mode (press 'q' to quit)..."
+	@if [ ! -d "node_modules" ]; then \
+		echo "❌ Dependencies not installed. Run 'make install' first."; \
+		exit 1; \
+	fi
+	npm run test:watch
+
+test-coverage:
+	@echo "Running tests with coverage..."
+	@if [ ! -d "node_modules" ]; then \
+		echo "❌ Dependencies not installed. Run 'make install' first."; \
+		exit 1; \
+	fi
+	npm run test:coverage
+	@echo "📊 Coverage report generated in coverage/ directory"
+
+test-ui:
+	@echo "Opening test UI in browser..."
+	@if [ ! -d "node_modules" ]; then \
+		echo "❌ Dependencies not installed. Run 'make install' first."; \
+		exit 1; \
+	fi
+	npm run test:ui
+
+# Development server (simple HTTP server for testing)
+serve:
+	@if command -v python3 >/dev/null 2>&1; then \
+		echo "Starting development server on http://localhost:8000..."; \
+		echo "📂 Serving files from current directory"; \
+		echo "Press Ctrl+C to stop"; \
+		python3 -m http.server 8000; \
+	elif command -v python >/dev/null 2>&1; then \
+		echo "Starting development server on http://localhost:8000..."; \
+		echo "📂 Serving files from current directory"; \
+		echo "Press Ctrl+C to stop"; \
+		python -m SimpleHTTPServer 8000; \
+	elif command -v npx >/dev/null 2>&1; then \
+		echo "Starting development server with npx..."; \
+		npx serve -l 8000; \
+	else \
+		echo "❌ No suitable HTTP server found"; \
+		echo "Install Python or Node.js to use 'make serve'"; \
+		exit 1; \
+	fi
+
+# Code quality (placeholder targets for future use)
+lint:
+	@if [ -f "package.json" ] && npm list eslint >/dev/null 2>&1; then \
+		echo "Running ESLint..."; \
+		npx eslint *.js; \
+	else \
+		echo "ℹ️  ESLint not configured. Skipping lint check."; \
+		echo "   To add linting: npm install --save-dev eslint"; \
+	fi
+
+format:
+	@if [ -f "package.json" ] && npm list prettier >/dev/null 2>&1; then \
+		echo "Formatting code with Prettier..."; \
+		npx prettier --write "*.js" "test/*.js"; \
+	else \
+		echo "ℹ️  Prettier not configured. Skipping code formatting."; \
+		echo "   To add formatting: npm install --save-dev prettier"; \
+	fi
+
+# Dependency management
+deps-check:
+	@echo "Checking for outdated dependencies..."
+	npm outdated
+
+deps-update:
+	@echo "Updating dependencies..."
+	npm update
+	@echo "✅ Dependencies updated"
+
+deps-audit:
+	@echo "Running security audit..."
+	npm audit
+	@echo "🔒 Security audit complete"
+
+# Cleanup
+clean:
+	@echo "Cleaning up..."
+	@if [ -d "node_modules" ]; then rm -rf node_modules && echo "🗑️  Removed node_modules/"; fi
+	@if [ -d "coverage" ]; then rm -rf coverage && echo "🗑️  Removed coverage/"; fi
+	@if [ -d ".vitest" ]; then rm -rf .vitest && echo "🗑️  Removed .vitest/"; fi
+	@echo "✅ Cleanup complete"
+
+# Quick setup for new developers
+setup: clean install test
+	@echo ""
+	@echo "🎉 Setup complete! You can now:"
+	@echo "   • Run 'make test' to run tests"
+	@echo "   • Run 'make test-watch' for TDD"
+	@echo "   • Run 'make serve' to start development server"
+	@echo "   • Open index.html in browser to use the app"