feat: add CMTAT standard and link five use cases to existing approaches

[mzf11125]

What are you adding

• Update to existing content
• Enterprise Use Case

Description

Two small pieces of work picked up from the open issue list.

CMTAT standard, closes #174

CMTAT is CMTA's open standard for tokenizing financial instruments. It plays a similar role to ERC 3643, already documented in this repo, but through a rule engine and allowlist model rather than an identity registry with claim issuers. It is blockchain agnostic, with reference implementations on EVM, Tezos, and Solana, and notably an existing privacy preserving implementation in Noir for Aztec.

Added as a cross referenced standard rather than a new pattern card, since the compliant tokenization intent is already covered by pattern erc3643 rwa.md and a near duplicate card would be redundant.

Files touched: GLOSSARY.md, patterns/pattern-erc3643-rwa.md, use-cases/private-rwa-tokenization.md

Approach coverage gaps, part of #138

Issue #138 tracks 14 use cases without a linked approach. Checking current file state, 4 were already effectively covered before this PR (private corporate bonds and private government debt through approach private bonds related_use_cases, private payments already linking out, and private supply chain through open PR #184).

This PR handles the remaining cheap extensions, linking each use case to an existing approach as an explicit variant, following the same pattern already used for private corporate bonds and private government debt.

private stocks, private commodities, private fx, and private repo now point to approach-private-trade-settlement.md
private treasuries now points to approach-private-payments.md

The five use cases that need a brand new approach card written from scratch (private messaging, private oracles, private read, private registry, private procurement) are intentionally left out of this PR for a follow up, given the scope of writing a full approach card per use case.

Files touched: use-cases/private-stocks.md, private-commodities.md, private-fx.md, private-repo.md, private-treasuries.md, approaches/approach-private-trade-settlement.md, approaches/approach-private-payments.md

Checklist

• I've checked this doesn't duplicate existing content
• All links work, verified with npm run validate
• Info is accurate

[mzf11125]

All CI green, ready for review @rymnc