fix(sense): gate role: attendee on meeting_detected and clamp in participation
Tighten contamination guard in talent/sense.md: role: attendee now explicitly requires meeting_detected: true for the same segment; otherwise every Person is role: mentioned.
Add a Python clamp in talent/participation.post_process: when no contributing sense segment has meeting_detected: true, rewrite every role: attendee entry to role: mentioned. Missing/unreadable sense.json collapses to False. One warning per affected record.
Cover with tests/test_sense_contamination_guard.py (prompt-presence + runtime clamp + idempotence + missing-file fallback).