test: replace external standards fixture

[swernerx]

Summary

• replace the external standards-test-repo2 consumer canary with a versioned in-repository GitHub consumer fixture
• add end-to-end coverage for upgrading standards 0 → 7, GitHub workflow selection, consumer-owned config preservation, clean checks, and idempotent re-application
• update historical notes to document the archived external fixture and the remaining live-integration boundary

Why

The dedicated external repository duplicated state and required manual cross-repository coordination. A checked-in fixture covers the deterministic consumer behavior directly in the standards test suite. Actual GitHub repository settings, Actions execution, Renovate scheduling, and cross-repository PR behavior remain intentionally outside the local test boundary.

Validation

• CI=true pnpm agent:check
• 77 tests passing
• lint, formatting, typecheck, build, and standards self-check passing

[greptile-apps]

Greptile Summary

This PR replaces an external consumer canary with a versioned local fixture and expands deterministic upgrade coverage.

• Adds a GitHub consumer fixture starting at standards version 0.
• Tests platform-specific workflow selection, consumer-owned configuration preservation, clean checks, and idempotent re-application.
• Updates historical documentation to identify the archived fixture and clarify the remaining live-integration boundary.

Confidence Score: 5/5

The PR appears safe to merge, with the new fixture resolving correctly under the repository’s test execution model and exercising the intended mechanical consumer upgrade.

The changes are confined to tests, fixtures, and historical documentation; the fixture is copied from the source test directory, the assertions match the current manifest and apply/check behavior, and no concrete regression or security issue was identified.

Important Files Changed

Filename	Overview
test/standards.test.ts	Adds a source-relative fixture copier and end-to-end upgrade test consistent with the repository's Vitest execution and apply/check contracts.
test/fixtures/github-consumer/.repometa.json	Defines a private GitHub consumer at standards version 0, enabling the intended full mechanical migration path.
test/fixtures/github-consumer/package.json	Provides Node-scope detection while remaining consumer-owned and unchanged by standards application.
test/fixtures/github-consumer/renovate.json	Provides an existing seeded configuration used to verify preservation of consumer-owned content.
test/fixtures/README.md	Accurately documents the deterministic behaviors covered by the fixture and the live-service behaviors left outside the test boundary.
changes/0003-platform-aware-ci.md	Replaces obsolete external-fixture coordination notes with the archived-repository and local-fixture status.
changes/0004-ci-workflow-forgejo.md	Updates historical fixture notes without changing the documented migration behavior.

_{Reviews (1): Last reviewed commit: "test: replace external standards fixture" | Re-trigger Greptile}