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>

test/setup.js

@@ -0,0 +1,39 @@
+// Test setup file for Vitest
+import { vi } from 'vitest'
+
+// Mock PapaParse (since it's loaded via CDN)
+global.Papa = {
+  parse: vi.fn()
+}
+
+// Mock fetch for loading files
+global.fetch = vi.fn()
+
+// Setup DOM helpers
+beforeEach(() => {
+  // Reset DOM
+  document.head.innerHTML = ''
+  document.body.innerHTML = ''
+
+  // Clear all mocks
+  vi.clearAllMocks()
+})
+
+// Create helper functions for DOM setup
+export const createMockElement = (tagName, attributes = {}) => {
+  const element = document.createElement(tagName)
+  Object.entries(attributes).forEach(([key, value]) => {
+    element.setAttribute(key, value)
+  })
+  return element
+}
+
+export const setupBasicDOM = () => {
+  document.body.innerHTML = `
+    <div id="projectName"></div>
+    <div id="projectSubtitle"></div>
+    <div id="viewer"></div>
+    <link id="dynamicCss" rel="stylesheet" href="">
+    <button id="downloadSvg"></button>
+  `
+}