Showcase: mark agentoracle-verifiable-delivery as withdrawn (AgentOracle is now Tanilo)

[TKCollective]

AgentOracle is now Tanilo. This showcase called our API gateway's POST /v1/compose, which signed a composed envelope over a verdict the caller supplied, without evaluating it. We withdrew that route on 24 September 2026 (it returns 410 since 28 September), so the showcase no longer works, and its example receipt was signed through that route. Full account: https://tanilo.io/incidents/2026-08-25-canned-verdicts

This PR adds a dated notice at the top of the showcase README and SKILL.md saying it is withdrawn, links the incident record, and notes the rename. Nothing else changes; the historical files stay in place.

If you'd prefer, I can instead remove the showcase or rebuild it against our /evaluate route, which evaluates the claim before signing. Your call. @LauJoeYing

[github-actions]

Thanks for being so proactive about this and for the clear write-up in the notice and the incident report. This is a great example of responsible maintenance.

The PR itself looks perfect — the notices are clear and well-placed.

Regarding your question about whether to mark as withdrawn, remove, or rebuild: that's a great question for the maintainers. Personally, I think there's value in keeping the historical entry with this notice, as the pattern is still instructive. But they'll have the final call on the content strategy.