[Idea] Let users use F2 shortcut to quickly rename sessions

Ideally, the user should be able to hit F2 or any rename shortcuts so they can quickly rename sessions, which will help a lot if a user has a lot of sessions going on.

The issue names no files, tests, or entry points. Start by locating the session-renaming UI and the application's keyboard shortcut handling, then determine how a rename shortcut should interact with existing session focus and editing behavior. Done means users can invoke renaming with F2 or an agreed shortcut and complete the rename reliably.

索引モデルが issue の本文から書いたものです。