feat(DEN-4080): execute production peer-authority contract parity

[ORESoftware]

Summary

Convert this repository from a suite-declaration stub into an executable sibling-organization acceptance action for ores-chat/ores-chat-interfaces.

The new action:

• accepts the caller's existing production checkout, so no private cross-org checkout token is needed;
• snapshots independently authored TypeSpec A, JSON Schema A, and the independent instance corpus;
• requires Draft 2020-12 schemas, isolated generated evidence, regular files, and no symlinked authority inputs;
• invokes ORESoftware/typespec-json-schema-validator@282883afc4645f3303ed746bdb1e1571475724c5 so TypeSpec emits comparison-only JSON Schema B without modifying JSON Schema A;
• optionally executes the production Rust parity slices;
• proves all authored input bytes are unchanged and emits a deterministic sibling-org receipt.

Tests

• 6 standard-library guard regressions;
• compiler-backed convergent fixture using the real immutable validator action;
• deliberately drifted required-field fixture that must fail closed;
• JSON, SARIF, source-digest, and sibling-org receipt retention.

Boundaries

contract-only remains accurate. This PR does not claim deployed endpoint coverage, does not introduce credentials, and does not make the test org a schema authority.

Closes #1.
Linear: DEN-4080