Add a CI docs-drift check between fixture files and transactions/README.md

[knytcomics-ui]

Problem

transactions/README.md manually documents which destinations.json addresses/labels appear in each XDR file. There's currently no automated check that this table stays in sync with reality when either the fixtures or the XDRs change — a change to one side with no corresponding update to the other passes CI silently today.

Requirements

• Build on the "referential integrity" and "describe-transactions" tooling from other issues in this batch: add a CI job that decodes every XDR, resolves each referenced address against destinations.json to get its current label, and compares that against what transactions/README.md's table claims for that file.
• Fail with a specific diff (e.g. "payment.xdr destination is labelled suspicious in destinations.json but README says malicious") if they disagree.
• This should be a genuinely new CI job, not a duplicate of the referential-integrity validation issue, which only checks existence, not label-accuracy of the documentation.

Acceptance Criteria

• Deliberately changing a destination's label in destinations.json without updating transactions/README.md fails this new CI check with a precise mismatch message.
• Passes on current main once the table and fixtures are confirmed consistent.

Part of the Gryd-lock organization. This repo supplies the labelled testnet fixtures and stub scores consumed by grydlock-oracle-adapter's StubOracle and evaluated end-to-end by grydlock-research.