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/testHelpers.js

@@ -0,0 +1,70 @@
+// Test helpers and utilities
+
+export const createSampleProject = () => ({
+  name: "Test Project",
+  description: "A test project for unit testing",
+  dataSource: "test.csv",
+  stylesheet: "test.css",
+  svgTemplate: "test.svg",
+  settings: {
+    timelineMonths: 12
+  },
+  fieldMapping: {
+    id: "ID",
+    title: "Title",
+    lane: "Lane",
+    due: ["Due"]
+  }
+})
+
+export const createSampleItems = () => [
+  {
+    id: "T-1",
+    title: "First Task",
+    lane: "Development",
+    due: new Date("2025-01-15")
+  },
+  {
+    id: "T-2",
+    title: "Second Task",
+    lane: "Testing",
+    due: new Date("2025-02-20")
+  },
+  {
+    id: "T-3",
+    title: "Third Task",
+    lane: "Development",
+    due: new Date("2025-03-10")
+  }
+]
+
+export const createSampleCSV = () => `ID,Title,Lane,Due
+T-1,First Task,Development,2025-01-15
+T-2,Second Task,Testing,2025-02-20
+T-3,Third Task,Development,2025-03-10`
+
+export const createSampleTemplate = () => `<svg xmlns="http://www.w3.org/2000/svg">
+  <rect width="100%" height="100%" fill="#FFFFFF"/>
+  {{MONTHS}}
+  {{LANES}}
+</svg>`
+
+export const mockFetch = (data, ok = true) => {
+  global.fetch.mockResolvedValueOnce({
+    ok,
+    json: () => Promise.resolve(data),
+    text: () => Promise.resolve(typeof data === 'string' ? data : JSON.stringify(data))
+  })
+}
+
+export const expectElementToHaveText = (selector, text) => {
+  const element = document.querySelector(selector)
+  expect(element).toBeTruthy()
+  expect(element.textContent).toContain(text)
+}
+
+export const expectSVGToContain = (selector, expectedContent) => {
+  const svg = document.querySelector(selector)
+  expect(svg).toBeTruthy()
+  expect(svg.outerHTML).toContain(expectedContent)
+}