feat: add tmux wrapper package for session operations
Session lifecycle:
- NewSession, KillSession, HasSession, ListSessions, RenameSession
Session interaction:
- SendKeys, SendKeysRaw, CapturePane, CapturePaneAll, AttachSession
Environment and windows:
- SetEnvironment, GetEnvironment, SelectWindow, GetSessionInfo
Error handling:
- Detects ErrNoServer, ErrSessionExists, ErrSessionNotFound
- Graceful handling when no tmux server running
Closes gt-u1j.4
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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