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>

vitest.config.js

@@ -0,0 +1,18 @@
+import { defineConfig } from 'vitest/config'
+
+export default defineConfig({
+  test: {
+    environment: 'jsdom',
+    globals: true,
+    setupFiles: ['./test/setup.js'],
+    coverage: {
+      provider: 'v8',
+      reporter: ['text', 'json', 'html'],
+      exclude: [
+        'node_modules/',
+        'test/',
+        '**/*.config.js'
+      ]
+    }
+  }
+})