Split StdinBuffer's incomplete-sequence wait from the lone-ESC wait so SSH and PI_TUI_ESC_TIMEOUT can reassemble split Alt+Enter without delaying Escape or mouse/CSI buffering.
* fix(tui): prevent split Alt+Enter from interrupting
Increase the escape-sequence timeout over SSH and allow high-latency terminals to override it with PI_TUI_ESC_TIMEOUT.
Fixes#7876
* docs(coding-agent): shorten escape timeout description
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Co-authored-by: Mario Zechner <badlogicgames@gmail.com>