Add `/delegate` — Create PR from session changes

[PureWeen]

Summary

The CLI's /delegate command sends the session's work to GitHub, where Copilot creates a PR from the changes. This is a one-click "ship it" action.

CLI Behavior

• /delegate — packages session changes and delegates to GitHub
• GitHub Copilot creates a PR with the session's file modifications
• Includes session context as PR description

SDK Events

• SessionHandoffEvent — session handed off to GitHub (includes source, context, repository info)

Proposed Implementation

1. "Create PR" button in session toolbar
2. Pre-submit preview — show files changed, proposed branch name, PR title
3. Progress indicator — track handoff status via SessionHandoffEvent
4. Link to PR — open the created PR in browser when done

Priority: 🟢 LOW