fix(protocol): align retry_after with the canonical error shape

[bokelley]

Summary

• align every maintained main-line reference with canonical top-level error.retry_after
• correct the idempotency/rate-limit runner contracts and reviewer guidance
• make RATE_LIMITED and IDEMPOTENCY_IN_FLIGHT metadata explicit about wire placement
• remove unsupported integer-only wording without changing the canonical number schema

Why

Prose and compliance assets referenced error.details.retry_after, while core/error.json defines retry_after on the error object itself. The rate-limit harness therefore risked rejecting conformant sellers and rewarding the wrong wire shape.

Validation

• schema validation
• storyboard test kits, documentation parity, and check-enum tests
• schema, compliance, and protocol-tarball builds
• error-code drift and immutable-artifact checks
• changeset scope/status checks
• TypeScript and git diff --check

The separate number-versus-integer decision is tracked in #5953.

Main-line portion of #5948.

[aao-secretariat]

Argus is not auto-reviewing this PR because it modifies protected paths that require human review (static/schemas/source/enums/error-code.json, static/schemas/source/protocol/get-adcp-capabilities-response.json). A human reviewer should review and merge this PR; Argus will resume on subsequent PRs once these changes land on main.

[aao-secretariat]

Argus is not auto-reviewing this PR because it modifies protected paths that require human review (static/schemas/source/enums/error-code.json, static/schemas/source/protocol/get-adcp-capabilities-response.json). A human reviewer should review and merge this PR; Argus will resume on subsequent PRs once these changes land on main.

[andybevan-scope3]

This PR contains a single change - looks good to me

Problem: Our guidance told developers to read the “wait this long before trying again” hint from a different place than where the actual rules said to put it, so anyone following the instructions would look in the wrong spot and miss the hint entirely.
Fix: All the guidance and examples were updated to point at the one correct, standard location where that retry hint actually lives.