When running `gt crew at` from inside tmux:
- No longer auto-links the target session as a tab
- Just prints "Started X. Use C-b s to switch."
- User stays in their current pane
When running from outside tmux:
- Default: attach to the session (existing behavior)
- With -d/--detached: start session without attaching
This gives users more control over tmux session navigation and
reduces confusion for tmux newcomers.
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>