docs(interop): portable signed records crosswalk

[jithinraj]

Summary

Adds an informative crosswalk that maps existing PEAC examples and recipes to the external evaluation, audit,
transparency, authorization, and security contexts where portable signed records are useful. It is a single
docs-only addition: docs/interop/PORTABLE-SIGNED-RECORDS-CROSSWALK.md.

Scope

Docs-only. No schema, registry, type URI, wire format, signing, public API, examples, generated artifacts,
facts.json, build_targets, or release-state change. Every row points at a PEAC artifact that already exists
in this repository; every relative link resolves on disk.

PR-4 (the evidence-primitive standards note) is intentionally not included in this PR.

What it contains

• A context map (8 rows) from each external context to the existing PEAC artifact that is relevant to it:
  AI agent standards and evaluation, EU AI Act record-keeping, evaluation tool outputs, open-model deployments,
  agent authorization and commerce intent, MCP and agentic infrastructure, LLM and application security
  evidence, and transparency receipts.
• A sources-and-boundaries table that cites each context from its own official or primary source, with a
  "Last checked" date and a neutral boundary statement per row.

Boundaries

The doc is descriptive. It states plainly that PEAC composes with adjacent standards and systems and does not
replace them; that it records observations while upstream systems remain responsible for their own behavior; and
that inclusion does not imply endorsement, support, adoption, partnership, or conformance. The transparency-
receipts row notes that SCITT is an in-process Internet-Draft effort and asks the reader to verify current
status at the source.

Validation

• All linked artifacts verified to exist; relative links resolve.
• entry-links-doc-truth and the public-artifact and planning-leak checks pass.
• pnpm lint (0 errors) and pnpm typecheck:core pass; git diff --check clean.
• Sources were re-verified against their official pages before authoring; the "Last checked" date reflects that.

[jithinraj]

Amended on the same branch to:

• Normalize the file to UTF-8 / LF with no hidden, bidirectional, zero-width, or control characters (verified locally; the file is plain ASCII with normal markdown line structure).
• Use the OSI Open Source AI Definition 1.0 as the generic, vendor-neutral source for the open-model row.
• Scope the FIDO row to its public materials and to recording execution evidence after an authorization or intent artifact exists.
• Note that SCITT architecture is in the RFC Editor / Datatracker process; verify current status at the source.
• Soften the opening wording and use "release processes".

Docs-only; all link-truth, public-artifact, planning-leak, lint, typecheck, and final-hygiene gates pass.