#9151: Docs: add freeCodeCamp OpenClaw full tutorial to showcase

Adds the [freeCodeCamp.org full tutorial](https://www.youtube.com/watch?v=n1sfrc-RjyM) to the showcase section. **Video:** OpenClaw Full Tutorial for Beginners – How to Set Up and Use OpenClaw (ClawdBot / MoltBot) (~55m) <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> Adds a new entry to the docs showcase page (`docs/start/showcase.md`) highlighting the freeCodeCamp.org “OpenClaw Full Tutorial for Beginners” video, including an embedded YouTube (nocookie) iframe and a direct “Watch on YouTube” link. Change is consistent with the existing “OpenClaw in Action” section’s pattern for other videos (responsive iframe wrapper + link). <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk. - Docs-only change that follows existing embed/link patterns in the same file; no build, runtime, or security-sensitive code paths are affected. - No files require special attention <!-- greptile_other_comments_section --> _{(3/5) Reply to the agent's comments like "Can you suggest a fix for this @greptileai?" or ask follow-up questions!} <!-- /greptile_comment -->