Fill more gaps with sessions

From @digitarald The skill calls out the specific set of tools and how to use them: https://github.com/github/github-app/blob/main/src-tauri/app-skills/orchestrate/SKILL.md

We've got some parity: App  create_session  /  send_session_message  /  get_session  correspond to VS Code  create_session  /  send_message  /  list_sessions  +  get_session_context , and  my PR adds matching creator coordination and idle notifications.

But the App skill expects capabilities VS Code doesn’t yet expose, such as project discovery, branching/forking, plan approval, and PR/issue sessions.