feat(signal,engine): ADR-137 calibration-mismatch contradiction + trust witness

- signal: MultistaticFuser::fuse_scored_calibrated() threads per-node
  CalibrationId; agreeing epochs → calibration_id set + CalibrationApplied
  evidence; disagreeing → calibration_id None + CalibrationIdMismatch flag
  (forces demotion). +2 tests.
- engine: process_cycle_calibrated() per-node calibration path; process_cycle
  delegates with a uniform epoch. TrustedOutput gains a deterministic BLAKE3
  witness over (provenance || class). calibration_version='cal:none' on mismatch.
- ADR-137 acceptance test: two frames + mismatched calibration -> QualityScore
  contradiction -> Restricted -> calibration_id None -> witness stable. +happy path.
- 11 engine tests, signal 411+ lib tests; workspace 0 errors.

Co-Authored-By: claude-flow <ruv@ruv.net>