Include branch refs in revision history response

[JohnRDOrazio]

Description

The revision history endpoint (/api/v1/projects/{id}/revisions) needs to return a refs map (commit hash → branch names) so the frontend can display branch labels on the git history graph and assign commits to separate visual lanes by branch.

Context

This is the backend counterpart to the frontend issue and PR:

• Frontend issue: Git history graph does not show branches since bare repo migration ontokit-web#8 — Git history graph does not show branches since bare repo migration
• Frontend PR: Show branch topology in revision history graph ontokit-web#10 — Show branch topology in revision history graph

The frontend consumes the refs field from the revision history response to visually separate branch commits onto different lanes and render branch name badges.

Solution

Add a refs field (Record<string, string[]>) to RevisionHistoryResponse that maps commit hashes to their associated branch names. Build the map by listing branches and matching their tip commits against the revision history.