Session exit should be silent by default

When a session ends, Claude Code prints:

Resume this session with:
claude --resume <session-id>

This should not be printed by default. The information is redundant — claude --list and --continue already provide access to past sessions. Printing a raw UUID on every exit adds noise without value.

Beyond being redundant, this message actively harms the experience for some users. It frames every session exit as loss — implying the session will be forgotten unless the user copies the ID. This creates unnecessary anxiety, especially for users who run many concurrent sessions and already have resumption as part of their workflow.

Proposal:

1. Remove the resume hint from default exit output — exit should be clean and silent.
2. Optionally, add a setting (e.g., "exit_message": "none") for users who want to suppress all exit output, in case future versions add other exit messages.