Git: commit history / log view

[Oaklight]

Problem

The Git tab shows current changes but no way to inspect past commits — what was changed when, by whom.

Proposed

• Sub-tab or expandable section in Git pane: 'History'
• Backend: GET /api/git/log?limit=50&path=<optional> returning JSON of commits (hash, author, date, message, files)
• Frontend: scrollable list; click commit → show its diff (reuses #git-diff renderer)

Notes

Builds on top of git diff viewer (#11). Keep paging / virtualization in mind for large repos.

Priority: P2