Exit prompt for named worktree sessions keeps its wording

A worktree is a separate copy of your project's files that Claude Code can work in. When you leave a worktree session you gave a name, Claude Code says the session was named after your chosen name and suggests: "Keep the worktree to resume it later, or remove it to clean up." The code that builds this message was rebuilt so that sentence is always included. It also fixes a mix-up in which the message was stored under a different name than the one used to show it.