feat: enhance skill-development description with stronger triggers

Add 8 new trigger phrases to improve skill activation:
- "SKILL.md format", "skill frontmatter", "skill triggers"
- "trigger phrases for skills", "progressive disclosure"
- "skill references folder", "skill examples folder", "validate skill"

Also expanded keyword coverage: file organization, writing style.

Total trigger phrases: 13 (was 5)
Character count: 484 (under 1024 limit)

Fixes #3

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: sjnims

plugins/plugin-dev/skills/skill-development/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: skill-development
-description: This skill should be used when the user asks to "create a skill", "add a skill to plugin", "write a new skill", "improve skill description", "organize skill content", or needs guidance on skill structure, progressive disclosure, or skill development best practices for Claude Code plugins.
+description: This skill should be used when the user asks to "create a skill", "add a skill to plugin", "write a new skill", "improve skill description", "organize skill content", "SKILL.md format", "skill frontmatter", "skill triggers", "trigger phrases for skills", "progressive disclosure", "skill references folder", "skill examples folder", "validate skill", or needs guidance on skill structure, file organization, writing style, or skill development best practices for Claude Code plugins.
 version: 0.1.0
 ---