fix: restructure skills directory for Claude Code compatibility

Move skills from flat files to subdirectories with SKILL.md:
- skills/itkdev-adr.md → skills/itkdev-adr/SKILL.md
- skills/itkdev-documentation.md → skills/itkdev-documentation/SKILL.md
- skills/itkdev-drupal.md → skills/itkdev-drupal/SKILL.md
- skills/itkdev-github-guidelines.md → skills/itkdev-github-guidelines/SKILL.md
- skills/itkdev-issue-workflow.md → skills/itkdev-issue-workflow/SKILL.md

Claude Code expects skills in subdirectories with a SKILL.md file,
matching the structure used by official plugins (frontend-design, etc.)

Closes #17

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: cableman

CHANGELOG.md

@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Skills not loading due to incorrect directory structure (#17)
+  - Restructured skills from flat files (`skills/skill-name.md`) to subdirectories (`skills/skill-name/SKILL.md`)
+  - Matches Claude Code's expected plugin structure
+
 ## [0.3.0] - 2026-01-26
 
 ### Added