feat: cmux cross-reference detection via tree TTY

[grimmerk]

Summary

cmux cross-reference for detection layer: fixes purple dot for bare claude or claude -r sessions with in-session /rename, same concept as iTerm2 cross-reference (PR #62).

How it works

Uses cmux CLI tree --all output which now includes a tty= field per surface (requires cmux PR: manaflow-ai/cmux#TBD):

1. Check if cmux is running (pgrep -x cmux)
2. Parse tree --all output for surfaces with tty= field
3. For each cwd-fallback claude PID: ps -o tty= → match against cmux surface TTYs → get surface title
4. Match surface title against custom titles → find correct session ID
5. Correct PID-session mapping if needed

Test proof

Tested with cmux dev build containing TTY support:

[cross-ref-cmux] parsed surfaces with TTY: 4
  ttys021→"✳ Claude Code", ttys010→"✳ hi codex-ff 16", ttys006→"~/git/fred-ff", ttys020→"grimmer@MacBookAirK15:~/git/codex-ff"
[cross-ref-cmux] corrected PID 30689: b24197ae... → d34b3d48... (surface: "✳ hi codex-ff 16")

Purple dot correctly stayed on the /rename'd session after closing the other same-cwd session.

Dependencies

• cmux: needs per-surface TTY in tree --all output (PR pending at manaflow-ai/cmux)
• Without the cmux change, tree --all has no tty= field → cmuxSurfaces is empty → cross-reference gracefully skips

Related: #60, #63

🤖 On behalf of @grimmerk — generated with Claude Code