Initial project setup

Add project structure with package.json, source code, tests, documentation, and GitHub workflows.

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

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

tests/setup.js

@@ -0,0 +1,66 @@
+/**
+ * Jest Test Setup
+ * Configure testing environment for YT2AI Bookmarklet
+ */
+
+// Mock performance API with proper Jest mocks
+const performanceMocks = {
+  now: jest.fn(() => Date.now()),
+  mark: jest.fn(),
+  measure: jest.fn()
+};
+
+global.performance = performanceMocks;
+
+// Ensure window.performance is available
+window.performance = global.performance;
+
+beforeEach(() => {
+  // Reset DOM
+  document.head.innerHTML = '';
+  document.body.innerHTML = '';
+  document.body.style.overflow = '';
+  
+  // Reset window properties
+  delete window.__YT2AI_INITIALIZED__;
+  delete window.__YT2AI_VERSION__;
+  delete window.__YT2AI__;
+  
+  // Reset performance mocks
+  performanceMocks.mark.mockClear();
+  performanceMocks.measure.mockClear();
+  performanceMocks.now.mockClear();
+  
+  // Clear module cache to allow fresh requires
+  jest.resetModules();
+});
+
+afterEach(() => {
+  // Clear timers
+  jest.clearAllTimers();
+  
+  // Clear mocks
+  jest.clearAllMocks();
+});
+
+// Global test utilities
+global.mockYouTubeUrl = (videoId = 'dQw4w9WgXcQ') => {
+  Object.defineProperty(window, 'location', {
+    value: {
+      href: `https://www.youtube.com/watch?v=${videoId}`,
+      hostname: 'youtube.com',
+      search: ''
+    },
+    writable: true
+  });
+};
+
+global.mockMobileEnvironment = () => {
+  Object.defineProperty(navigator, 'userAgent', {
+    writable: true,
+    value: 'Mozilla/5.0 (Linux; Android 10; SM-G975F) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.120 Mobile Safari/537.36'
+  });
+  
+  Object.defineProperty(window, 'innerWidth', { writable: true, value: 375 });
+  Object.defineProperty(window, 'innerHeight', { writable: true, value: 667 });
+};