v0.1.15

Fix message ordering root cause: WS event replay was creating duplicate assistant bubbles after history load. Added catchup mode - after history REST load completes with last turn ended, skip WS-replayed turn/start, assistant/chunk, turn/end, assistant/message events until a new user/message arrives or user sends via send(). Also: always finalize previous assistant bubble before adding user message, clean up empty bubbles from stale turn/end.