Auto-suggest opening a PR upon session completion

[dgershman]

Summary

When a session is completed and the worktree branch has commits ahead of main, automatically suggest or prompt the user to open a PR.

Details

• Detect when a session transitions to completed status
• Check if the worktree's feature branch has unpushed commits or commits ahead of the base branch
• Suggest creating a PR via notification, UI prompt, or automated action
• Should leverage existing ticket metadata (title, number, URL) to pre-fill PR details