naming ceremony: thickness-gated progressive unlock
Replace the onboarding-time naming step with a thickness-gated ceremony
that triggers only after the journal develops sufficient depth. Adds
compute_thickness() to awareness.py with five signals (entity_depth,
conversation_count, recall_success, facet_count, journal_days) and a
composite ready gate. The naming muse now requires thickness readiness
and default name_status before proposing, with proposal cap and cooldown.