Feat/three way merge

[DanisLol]

Summary

• Three-way merge on diverged branches
• Text conflicts write markers, leave refs unchanged, and persist pending merge state under .minigit/.
• Resolve with add then commit command using the saved parents

Validation

• scripts/quality-check.sh
• Manual testing, if applicable:

Checklist

• The change is focused and easy to review.
• Tests were added or updated for behavior changes.
• Documentation was updated for user-facing or setup changes.
• No secrets, generated artifacts, or local-only files are included.

Notes for Reviewers