feat(models): show line diffs in cube version history

[akshaykumar2505]

Summary

• Models Versions list now shows which files and lines changed versus the previous snapshot, plus a picker to compare any two versions.
• Restore opens a preview of the line diff versus the current models before creating the new version; the live row is tagged Current and is not restorable.
• Restored snapshots keep the full checksum, use a shared color when hashes match, and show a Restored from timestamp under the checksum.

Test plan

• Open Models, then Versions, and confirm Created at shows author, exact time, and relative time.
• Expand a revision and confirm only changed files open with added/removed lines highlighted.
• Use Compare From/To with two non-adjacent versions and confirm the line diff.
• Click Restore on an older version, confirm the preview vs current, then confirm restore creates a new top version tagged Current.
• Confirm the matching older checksum turns the same blue and shows Restored from the source timestamp under the new checksum.
• Confirm Restore is hidden on Current and on rows that already match the live checksum.

Made with Cursor