feat: Add testing infrastructure and documentation

- Set up Vitest for unit testing with jsdom
- Add test setup with Web Audio API and requestAnimationFrame mocks
- Create initial test suites for DOM and animations modules
- Add test scripts to package.json (test, test:ui, test:run, coverage)
- Update CI workflow to include test execution
- Create CONTRIBUTING.md with conventional commits guidelines
- Create SECURITY.md with security policy
- Update ESLint config to support test files
- All tests passing (8/8)

Co-authored-by: ZaneThePython <102631678+ZaneThePython@users.noreply.github.com>

tests/setup.js

@@ -0,0 +1,34 @@
+// Test setup file
+import { beforeEach, vi } from 'vitest';
+
+// Mock Web Audio API
+global.AudioContext = vi.fn().mockImplementation(() => ({
+  createOscillator: vi.fn().mockReturnValue({
+    connect: vi.fn(),
+    frequency: {
+      setValueAtTime: vi.fn(),
+      exponentialRampToValueAtTime: vi.fn(),
+    },
+    start: vi.fn(),
+    stop: vi.fn(),
+  }),
+  createGain: vi.fn().mockReturnValue({
+    connect: vi.fn(),
+    gain: {
+      setValueAtTime: vi.fn(),
+      exponentialRampToValueAtTime: vi.fn(),
+    },
+  }),
+  destination: {},
+  currentTime: 0,
+}));
+
+// Mock requestAnimationFrame
+global.requestAnimationFrame = vi.fn((callback) => setTimeout(callback, 16));
+global.cancelAnimationFrame = vi.fn(clearTimeout);
+
+// Reset DOM before each test
+beforeEach(() => {
+  document.body.innerHTML = '';
+  document.head.innerHTML = '';
+});