test(readFileTool): add comprehensive test coverage for readFileTool

- Add 44 new tests covering edge cases and untested code paths
- Tests for legacy path handling, handlePartial errors, getStartLine fallback
- Tests for getLineSnippet when lines exceed file length
- Tests for batch approval flow and media provider integration
- Tests for file path normalization and edge cases
- Total test count: 77 (was 33, added 44)

Author: proyectoauraorg