ERC-8262: jurisdiction policy table + tighter settlement_root

[DROOdotFOO]

Summary

Two pre-audit normative fixes for the in-flight ERC-8262 submission (ethereum#1747). Both land in the reference implementation repo as well; this PR brings the fork branch in sync.

F-2 -- Jurisdiction Policy as normative table

The current draft mentions requireSignedSignals and minMultiProviderThreshold only as parenthetical asides ("e.g. US BSA, Singapore, UAE VARA require M >= 2"). A reader implementing from the spec alone could ship without the rejection logic.

This PR adds a Jurisdiction Policy subsection right after the threshold table. It tabulates the canonical "Accepts unsigned" and "Min threshold_m" values per jurisdiction with MUST language. Three scattered prose asides are replaced with "(see Jurisdiction Policy)" cross-refs.

F-3 -- pattern.settlement_root binding strengthened to MUST

The Pattern proof bullet previously said consumers SHOULD mark each consumed pattern proof to prevent reuse. With only the SettlementRegistry as a downstream consumer demonstrating this, a future consumer could silently accept a single PATTERN attestation as a standin for the binding it expects.

This PR promotes SHOULD mark to MUST mark and adds the canonical computation keccak256(abi.encode(uint8 subTradeCount, bytes32[] subProofHashes)) mod BN254_FR_MODULUS. The note also calls out that field width or abi.encode byte layout drift produces a different root and the equality check rejects.

Notes

• F-1 (UAE jurisdiction) was already in the draft; no change here.
• F-4 (proofHash forward-ref) was already in the draft via the -- see Proof Hash Computation comment.
• The Jurisdiction column widths in the threshold table widened by 3 chars to fit "Singapore (MAS)"; the markdown renders identically either way.

After this lands, the fork branch and the reference implementation's ERC-8262.md are byte-equal.