Follow-up from #2173 review: short wrapped composer lines above the compose floor #2174

Codex P2 on #2173 (Sources/TranscriptedWriting/Core/Scene/ScreenScene.swift:507): when a compose field wraps across 3+ OCR blocks (short first line like ok, then two longer matching lines), the floor lands on the last line. The short first line is exempt from dedup and stays in conversationTurns as if it were an earlier message. Keep a cutoff that also drops short wrapped composer fragments while ignoring genuinely higher quoted echoes. Related: #2160.