edge/engine.py keyed the ghost cooldown as
(GHOST, round(x), round(y)) — purely spatial, ignoring track identity.
Two distinct workers collapsing at ~the same pixel within the cooldown
window would suppress each other's ghost event, potentially masking a
second CRITICAL incident.
edge/detectors/ghost.py GhostIncidentDetector.update now includes the
candidate's track_id in each emitted dict. edge/engine.py keys the
cooldown as (EventType.GHOST, track_id) and sets the emitted Event's
track_id accordingly, matching how FALL/NO_MOTION/IMMOBILITY/zone events
are already keyed per-track.
Tests: tests/test_ghost.py asserts ghosts[0]["track_id"] == 1 on the
existing reappear-timeout test.
