v0.31.0 — Section-role correctness and applicability as identity

The first half of SPEC-125, governed by ADR-028: correct the section-role data, and make attribute applicability a rune-structural fact that a theme cannot change.

Nothing here breaks a build. The user-visible outcome is that reading and dropcap start working on runes where they were silently dropped — most obviously card, whose content model is literally "body (optional, repeatable any block)" but whose sections map never declared the role.

The half that does break — narrowing schemas so an inapplicable attribute is rejected rather than ignored — is v0.32.0.