fix: Update elegant-design YAML frontmatter to use hyphen-case

Change name from 'Designing Elegant Interfaces' to 'elegant-design' to
match the validation requirements and be consistent with other skills.

The name field must use hyphen-case format (lowercase letters, numbers,
and hyphens only) to pass CI validation.

Fixes smoke test validation error.

Author: claude

skills/elegant-design/SKILL.md

@@ -1,5 +1,5 @@
 ---
-name: Designing Elegant Interfaces
+name: elegant-design
 description: Create world-class, accessible, responsive interfaces with sophisticated interactive elements including chat, terminals, code display, and streaming content. Use when building user interfaces that need professional polish and developer-focused features.
 ---