Adds a Device.listen capability (real + mock), an Observation/HeardNode
domain model, an observations table with Repository.record_observation /
heard_nodes aggregation, and a `monitor` tool that listens for a window and
logs every overheard advert/telemetry (SNR, RSSI, shared location) to the
database. This is the longitudinal substrate later features read back.
The real-hardware event-payload mapping is best-effort and, like the trace
mapping, flagged for validation against the firmware's event schema; the mock
device synthesizes plausible adverts so the tool and tests run without a radio.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Jean-Pierre MartineauandClaude Opus 4.8
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