Feature request: /exit should close only the current tab and ask for confirmation when multiple tabs are open

[steilerDev]

Problem

Running /exit kills all open sessions, not just the current tab. If you have multiple tabs open in parallel and close one that's done, you lose all the others.

This is a footgun: the intent is to close one session cleanly, but the outcome is losing all parallel work.

Proposed Behaviour

1. Single tab open: /exit closes the session immediately, current behaviour.
2. Multiple tabs open: /exit should either:
   • Close only the current tab and leave the others running, OR
   • Prompt for confirmation first (e.g. "You have 3 other sessions open. Close all? [y/N]") so the user can abort if they hit /exit by accident.

Option 1 (close only current tab) feels most natural — it matches how tabs work in every terminal emulator and browser.

Steps to Reproduce

1. Open 4 parallel agent sessions (e.g. 4 docker agent run tabs).
2. In one tab that has finished its task, type /exit.
3. All 4 sessions are killed.

Why It Matters

Parallel sessions are a core pattern for multi-agent workflows. Losing in-progress parallel work because you closed a finished tab is a significant productivity hit and data-loss risk (anything not yet persisted to the KB is gone).