Rollback point before dual-stream verify_calibration refactor

State at this tag:
- DACS sym3axis cal works (vehicle_magnetometer matches expected within ~1 uT)
- verify_calibration uses SCALED_IMU2 (raw) so cal effect not visible there
- Tag created before refactoring verify to read both raw + calibrated streams

Revert with:
  git reset --hard pre-verify-refactor-2026-04-29