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/01-ourdigital-brand-guide/docs/CHANGELOG.md

@@ -0,0 +1,32 @@
+# Changelog
+
+All notable changes to ourdigital-brand-guide will be documented here.
+
+## [1.0.0] - 2026-01-31
+
+### Added
+- Initial skill creation
+- Desktop and Code versions
+- Comprehensive brand foundation reference
+- Korean and English writing style guidelines
+- Complete color palette with CSS tokens
+- Channel-specific tone matrix
+- Brand compliance checking guidelines
+
+### Files
+- `desktop/SKILL.md` - Claude Desktop version
+- `code/SKILL.md` - Claude Code version
+- `shared/references/brand-foundation.md` - Complete brand identity
+- `shared/references/writing-style.md` - Writing guidelines
+- `shared/references/color-palette.md` - Visual identity
+- `shared/assets/tokens.css` - CSS variable system
+
+### Sources
+- https://www.ourdigital.org/brand-guide/
+- Notion: Our Digital Blog Styleguide
+- Notion: Brand Color Palette
+- Notion: OurDigital 브랜드 가이드 시스템 프레임워크
+- Notion: Summary - OurDigital 브랜드 가이드 및 웹 콘텐츠 프로젝트
+
+### Notion Ref
+- (To be synced)