SEO/GEO: add maintained public agent-skills discovery index

[replynodes-ai]

Context

Issue #6 audit: https://github.com/replynodes/seo-geo-growth-agent/blob/main/docs/issue-6-growth-audit.md
Evidence: https://github.com/replynodes/replynodes-agent-skills publicly describes ReplyNodes Agent Skill for OpenClaw, but no marketing-site link was verified in the bounded pass.

Deliverable

Create a public index/readme section listing skills, supported runtime/client, version, install source, permissions, and read-only/write boundaries; provide the canonical URL for site/docs linking.

Acceptance criteria

• Inventory is generated from repository contents or maintained with an owner and review date.
• Every listed skill has a source path and compatibility statement.
• No credential/telemetry/publishing claim is made without source evidence.
• Focused link/fixture checks pass.
• Owner: Agent skills maintainer.