Handle terminal resizing

[sjmiller609]

Note

Medium Risk
Touches interactive terminal/WebSocket concurrency; incorrect locking or message formatting could break TTY sessions or cause hangs under resize/input load.

Overview
Adds terminal sizing support to hypeman exec TTY sessions by including initial rows/cols in the exec request and sending {"resize":...} messages on SIGWINCH while running interactively.

Introduces a mutex to serialize concurrent WebSocket writes from stdin forwarding and resize events to avoid races/panics during interactive exec.

^{Written by Cursor Bugbot for commit 595a435. This will update automatically on new commits. Configure here.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is OFF. To automatically fix reported issues with Cloud Agents, enable Autofix in the Cursor dashboard.}