Incorporate Sightline calibration feedback

[Charlie-Wang-03]

Motivation

Calibration of dsh-sightline exposed three reusable engineering distinctions.

Change

• preserve meaningful Unknown / unavailable states instead of collapsing them into absence or failure;
• record explicit compatibility identities when implementation behavior depends on fast-moving external semantics;
• allow consumer-specific disclosure projections from a richer canonical internal representation when trust or purpose differs.

These refine existing Preferences and Project Conventions without adding new governance layers.

Validation

Run python3 scripts/validate_repo.py.