tmux session is destroyed on unexpected exit, losing error output

## Problem When CORAL exits unexpectedly while running inside tmux, the tmux session is destroyed. This makes it impossible to scroll back and check what error caused the crash. ## Expected behavior The tmux session should remain alive (or at least preserve its output) after an unexpected exit, so users can inspect the error message and stack trace. ## Possible solutions - Set `remain-on-exit on` for the tmux window/pane so it stays open after the process dies - Log fatal errors to a file (e.g. `.coral/crash.log`) in addition to stderr - Use `set-option destroy-unattached off` to prevent session teardown