fix: webchat round-trip correlation — use sessionKey fallback when conversationId missing

[maxdraki]

Problem

Webchat traces only show msg:received:webchat with 1ms duration. The hook correlates inbound→outbound by conversationId to compute real response time, but webchat does not populate conversationId.

Fix

The openclaw-hook now falls back to sessionKey when conversationId is absent, producing proper round-trip traces for webchat sessions.

Status

✅ Fixed in Night 7 (commit 0dfb7ae5, PR #1). Hook uses correlationKey() helper that prefers conversationId and falls back to sessionKey.