feat(sidebar): show git branch instead of worktree name

[neumie]

Summary

• Worktree entries in the sidebar now display the current git branch name instead of the stored project name
• Uses the existing non-blocking git status cache (populated by background poller), falling back to the project name if not yet cached

Changes

• Modified SidebarProjectInfo::from_project to resolve the branch from okena_git::get_git_status for worktree projects

Test plan

• Open Okena with a project that has worktrees
• Verify worktree entries in the sidebar show the branch name (e.g. feat/my-feature) instead of the directory or stored name
• Verify non-worktree projects still show their project name as before
• Verify that before git status cache populates, the fallback name is shown correctly