Add Diff View Before Comitting

<!-- Please use the GitHub issue tracker only for bug reports and smaller suggestions for improvements. Requests for completely new features, questions and general feedback is now handled at https://discourse.jabref.org. Thanks! --> **Is your suggestion for improvement related to a problem? Please describe.** I would like to have the option to see the diffs before committing. **Describe the solution you'd like** Using this type of display in addition to the commit message in the commmit dialog: <img width="1813" height="851" alt="Image" src="https://github.com/user-attachments/assets/1f052e46-07a1-415d-a521-f839621b0b12" /> **Additional context** Add any other context or screenshots about the feature request here.