feat(test): add comprehensive test suite and testing infrastructure

- Add vitest configuration with coverage reporting
- Create test setup file with DOM mocks
- Add tests for state management, helpers, and tool configurations
- Update tsconfig and package.json for testing support
- Clean up unused comments and improve code style

src/js/ui.ts

@@ -1,4 +1,3 @@
-// FILE: js/ui.js
 import { resetState } from './state.js';
 import { formatBytes } from './utils/helpers.js';
 import { tesseractLanguages } from './config/tesseract-languages.js';