Adds context menu actions to quickly filter the Commit Graph to show only commits from a selected branch or tag.

Impact

Users working with repositories containing many branches can now quickly focus the Commit Graph on a single branch or tag by right-clicking it and selecting "Solo Branch in Commit Graph" or "Solo Tag in Commit Graph". This eliminates the need to manually type ref: search queries, improving efficiency when investigating specific feature branches or release tags.

Validation

1. Open a repository with multiple branches and tags
2. Open the Commit Graph
3. Right-click any branch in the graph or in the Branches view
4. Select "Solo Branch in Commit Graph" from the context menu
5. Confirm the graph filters to show only that branch's commits with ref:branch-name applied to the search
6. Clear the search filter
7. Right-click a tag and select "Solo Tag in Commit Graph"
8. Confirm the graph filters to show only that tag's commits

Risk

Low — Adds new context menu commands that invoke existing graph search/filter functionality. No changes to core graph rendering or filtering logic.