feat: Add OurDigital custom skills package (10 skills)

Complete implementation of OurDigital skills with dual-platform support
(Claude Desktop + Claude Code) following standardized structure.

Skills created:
- 01-ourdigital-brand-guide: Brand reference & style guidelines
- 02-ourdigital-blog: Korean blog drafts (blog.ourdigital.org)
- 03-ourdigital-journal: English essays (journal.ourdigital.org)
- 04-ourdigital-research: Research prompts & workflows
- 05-ourdigital-document: Notion-to-presentation pipeline
- 06-ourdigital-designer: Visual/image prompt generation
- 07-ourdigital-ad-manager: Ad copywriting & keyword research
- 08-ourdigital-trainer: Training materials & workshop planning
- 09-ourdigital-backoffice: Quotes, proposals, cost analysis
- 10-ourdigital-skill-creator: Meta skill for creating new skills

Features:
- YAML frontmatter with "ourdigital" or "our" prefix triggers
- Standardized directory structure (code/, desktop/, shared/, docs/)
- Shared environment setup (_ourdigital-shared/)
- Comprehensive reference documentation
- Cross-skill integration support

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

custom-skills/10-ourdigital-skill-creator/docs/CHANGELOG.md

@@ -0,0 +1,26 @@
+# Changelog
+
+All notable changes to ourdigital-skill-creator will be documented here.
+
+## [1.0.0] - 2026-01-31
+
+### Added
+- Initial skill creation
+- Desktop and Code versions with YAML frontmatter
+- Interactive Q&A workflow for requirements gathering
+- Skill suitability evaluation criteria
+- Directory structure scaffolding scripts
+- Validation script for skill structure checking
+- Skill patterns and templates reference
+
+### Files
+- `desktop/SKILL.md` - Claude Desktop version
+- `code/SKILL.md` - Claude Code version
+- `shared/references/suitability-criteria.md`
+- `shared/references/skill-patterns.md`
+- `shared/templates/SKILL-TEMPLATE.md`
+- `shared/scripts/init_skill.py`
+- `shared/scripts/validate_skill.py`
+
+### Notion Ref
+- (To be synced)