schema-bound-tokens v0.3: §4.2 + §4.4 open questions

[proofmancer]

Tracks the §4.2 and §4.4 open questions from schema-bound-tokens v0.2.

• Cap-exceedance slash severity calibration (§4.2) — needs ligate-chain#51 slashing-module extension first. Severity-curve calibration awaits devnet data on observed cap-exceedance attempts (frequency, magnitude, attestor-set characteristics). Calibration spec lives in chain RFC; paper sets the framework.
• Sub-quorum partial mint mechanism (§4.4) — mint_quorum_threshold field deferred. Lets a sub-quorum of the attestor set issue partial mints below the cap. Sub-quorum proof carries through the attestor-set update mechanic (§2.4). Different threat surface from full mints.

Dependencies

• ligate-chain#51 (disputes / slashing module) for §4.2
• Devnet data for §4.2 calibration

Cross-references

• per-schema-fees v0.3 rollup (sponsorship model formalization is adjacent)
• ligate-chain#286 (engineering side of schema-bound-tokens)