ci: reject retired repository links in active documentation

[devantler]

🤖 Generated by the Agentic Engineer

Active README and agent instructions have no check preventing links to the already retired reusable-workflows repository. Immutable main 63a8515 has no consumer configuration or retired-link guard in CI.

Adopt the released, read-only shared Actions guard with explicit README.md and AGENTS.md scope, no historical exemptions, and include it in the required CI result. Verify the actual clean consumer scan, a seeded README link rejected with its expected diagnostic, and missing configuration rejected without a success verdict. Native CI must pass at the reviewed head and again after merge.

Part of devantler-tech/.github#269. This consumer adoption does not retire the shared opt-in or shorten its observation floor.

[devantler]

🤖 Generated by the Agentic Engineer

Post-merge documentation guard behavior is proven at merge 739d01b from PR #524. The push/main guard job 111754094391 completed successfully at 2026-10-05T12:28:05Z, and native checkout confirms that exact merged commit.

The immutable released action at bd0035dd8f41fcf1459b878882b8897443f8dc59 scanned the configured README.md and AGENTS.md files, found zero retired links or historical exceptions, and produced validated=true. The completed native assertion verified that output.

The subsequent control step built the real CLI from the same exact released source. Its disposable seeded README link returned exit 1 with the expected README/path/repository diagnostic; deleting the consumer config returned exit 2 with the invalid-configuration diagnostic. Both native assertions passed, followed by the control step's PASS message.

Native readback confirms this issue is Closed and its Project 5 status is Done. The separate whole-main-CI acceptance requirement is also complete: run 37307340098 is now completed with conclusion success, freshly verified at the same merged commit. The canonical #269 observation floor remains 2026-10-10T23:46:08Z.