## 1. Implementation

- [x] 1.1 Update FileNotFoundError error message in convert_akomantoso_to_markdown_improved()
- [x] 1.2 Test with invalid input like "legge stanca" to verify new message
- [x] 1.3 Test with valid inputs (URL, file, -s) to ensure no regression

## 2. Validation

- [x] 2.1 Run tool with invalid input and verify helpful error message
- [x] 2.2 Verify all three usage modes still work correctly
