#240 fix: correct poteto-mode skill identifier

Summary

Fix the poteto-mode skill identifier to comply with the documented Agent Skills/Cursor identifier requirements.

• Changed name: Poteto Mode to name: poteto-mode
• Preserved the human-readable display name as Poteto Mode
• node scripts/validate-plugins.mjs passes

Fixes #237

---

[!NOTE]
Low Risk
Frontmatter-only identifier fix with no runtime, auth, or data-handling changes.

Overview
Aligns the poteto-mode skill name with Agent Skills/Cursor identifier rules by changing it from Poteto Mode to poteto-mode.

Keeps the human-readable label as Poteto Mode via metadata.cursor-display-name.

^{Reviewed by Cursor Bugbot for commit 7c9e9321e663660e034c0b69a945c0cfb3e03440. Bugbot is set up for automated code reviews on this repo. Configure here.}