chore: tti and parse payload debug metrics

[shaunwarman]

Signature	Culprit
high queueWaitMs, small handlerMs	WebSocket/event-loop backlog before the handler
high directAppend / tmpDbOpen	SQLite stall (WAL checkpoint, LRU eviction churn)
all stages elevated in a burst	storm (backup contention / CPU saturation)
TTI directTimeout with no matching slow-payload line	stall upstream of parse-payload (MX/WSP leg)