[docs] Add troubleshooting for unauthorized messages in tmux (#61962)

[giruuuuj]

Summary

Adds a troubleshooting entry for unauthorized phantom messages appearing in tmux sessions. Documents the likely root cause (tmux forwarding control sequences interpreted as keypresses) and workaround (disable focus-events or run outside tmux).

Closes #61962

Problem

In v2.1.150 on macOS with tmux, messages may appear to be sent on the user's behalf without their input. The TUI input reader interprets terminal control sequences (focus events, bracketed paste) forwarded by tmux as actual keypresses or text input.

Workaround

Run outside tmux to confirm the trigger. In tmux, disable focus events:
set -g focus-events off

Related

• [BUG] System-generated messages misattributed as Human: turns during multi-agent team sessions, causing unauthorized autonomous actions #27128 / [BUG] Agent Teams: teammate idle notifications rendered as "Human:" turns — ghost messages cause unintended destructive actions #28627 � similar symptom (unauthorized messages) but different root cause (model generating fake Human: turns in multi-agent sessions)