feat(daemon): log checkpoint admission delayed behind trace ingestion

Checkpoint admission waits on the trace-ingest watermark; when that
watermark stalls, checkpoints sit "received into bounded ingress" with
no admission line, and the delay has to be inferred from absent logs
(as in #2252, where seq 77-84 were received but never admitted). Log
the wait explicitly once it exceeds five seconds, and again at that
cadence while it persists, including the receipt sequence, the target
and processed ingest sequences, and the total wait so far.

Refs #2252

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>