feat: enhance timeline navigation with comprehensive testing and documentation

- Add comprehensive test suite with 13 passing tests
- Create detailed keyboard shortcuts documentation (KEYBOARD_SHORTCUTS.md)
- Add meaningful code comments explaining functionality
- Set up Vitest testing framework with proper mocks
- Fix React imports in timeline components for proper JSX rendering
- Add ResizeObserver mock for browser environment compatibility
- Enhance keyboard shortcuts help to properly format Enter key display

Tests cover:
- Enter key keybinding functionality
- Return to Start button click behavior
- Keyboard shortcuts help system integration
- Component rendering and tooltip structure

Documentation includes:
- Complete keyboard shortcuts reference
- UI feature explanations
- Usage notes and behavior descriptions

All tests passing (13/13) with full feature coverage.

apps/web/vitest.config.ts

@@ -0,0 +1,15 @@
+import { defineConfig } from 'vitest/config'
+import { resolve } from 'path'
+
+export default defineConfig({
+  test: {
+    environment: 'jsdom',
+    setupFiles: ['./src/test/setup.ts'],
+    globals: true,
+  },
+  resolve: {
+    alias: {
+      '@': resolve(__dirname, './src'),
+    },
+  },
+})