docs: correct sendPendingCtrlL comment (it has no callers)

The prior wording claimed the no-op stub was kept so SSE idle/working
handlers could call it without guards, but there are no callers anywhere.
Reword to reflect that it's a vestigial, intentionally-retained guard
documenting why Ctrl+L must not be auto-sent. Comment-only; minified
build output is unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>