#22410: docs: Add Agent Cloud Memory to community skills

Adds a reference to [Agent Cloud Memory](https://github.com/lilyjazz/agent-cloud-memory) in the Skills documentation. This library provides serverless persistence capabilities (RAG, Teleport, etc.) powered by TiDB Zero. <!-- greptile_comment --> <h3>Greptile Summary</h3> Adds a new "Community Skill Libraries" section to the Skills documentation, introducing Agent Cloud Memory as a serverless persistence skill library. The section is well-positioned and clarifies that users can clone skill repositories directly into their workspace as an alternative to ClawHub. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with no issues found. - This is a straightforward documentation addition that follows existing patterns, uses proper markdown formatting, and is logically positioned within the document structure. No code changes, no breaking changes, and the content accurately describes an alternative way to use skills. - No files require special attention. _{Last reviewed commit: 0d63ba8} <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->