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>

package.json

@@ -5,7 +5,10 @@
   "scripts": {
     "dev": "next dev",
     "build": "next build",
-    "start": "next start"
+    "start": "next start",
+    "test": "jest",
+    "test:watch": "jest --watch",
+    "test:coverage": "jest --coverage"
   },
   "dependencies": {
     "next": "16.1.6",
@@ -15,9 +18,14 @@
   },
   "devDependencies": {
     "@tailwindcss/postcss": "^4",
+    "@testing-library/jest-dom": "^6.9.1",
+    "@testing-library/react": "^16.3.2",
+    "@types/jest": "^30.0.0",
     "@types/node": "^20",
     "@types/react": "^19",
     "@types/react-dom": "^19",
+    "jest": "^30.2.0",
+    "jest-environment-jsdom": "^30.2.0",
     "tailwindcss": "^4",
     "typescript": "^5"
   }