🧪 Add unit tests for utility functions

[baris-sinapli]

📝 Task

Add comprehensive unit tests for utility functions.

✅ What to do

• Test formatting functions (formatFileSize, formatTimeAgo)
• Test debounce utility
• Add edge case testing
• Ensure 100% coverage for utils

📍 Files to modify

• Create test files in src/lib/utils/
• Follow existing test patterns

🎯 Acceptance criteria

• All utility functions tested
• Edge cases covered
• Tests pass consistently
• Good test coverage

Estimated time: 2-4 hours