refactor: organize tests and extract formatting utilities

- Move test files to lib/__tests__/ directory
- Extract formatting utilities (formatVersion, formatFileSize, formatDateTime)
  from fs-utils.ts to new utils.ts module
- Add Jest test configuration and test scripts
- Update component imports to use new utils module
- Add CLAUDE.md documentation for project structure

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

jest.setup.js

@@ -0,0 +1,2 @@
+// Learn more: https://github.com/testing-library/jest-dom
+import '@testing-library/jest-dom'