fix(websocket): drop consumed compaction triggers

After remote compaction succeeds, the normalized previous request still contains the consumed compaction_trigger. The next WebSocket-to-HTTP merge replays that trigger before the compaction output and current input, causing the upstream 400 error.

Remove compaction_trigger only from previous request items when the previous response contains compaction or compaction_summary. Add a two-step regression test covering trigger normalization followed by compact replay.

Fixes #5041