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/06-ourdigital-designer/README.md

@@ -0,0 +1,80 @@
+# OurDigital Designer
+
+Visual storytelling and image prompt generation for OurDigital content.
+
+## Purpose
+
+Transform philosophical essays into sophisticated visual narratives:
+- Featured image prompts for AI art tools
+- Minimalist, conceptually rich designs
+- Korean-Western aesthetic fusion
+- Blog thumbnail optimization
+
+## Activation
+
+Only activates with "ourdigital" keyword:
+- "ourdigital design featured image"
+- "ourdigital 썸네일 만들어줘"
+- "ourdigital image prompt for [topic]"
+
+## Core Philosophy
+
+OurDigital images are visual philosophy—not illustrations but parallel texts that invite contemplation:
+
+- **Abstract metaphors** over literal representations
+- **Contemplative minimalism** with 20%+ negative space
+- **Cultural fusion** of Korean-Western aesthetics
+- **Emotional resonance** through color psychology
+
+## Structure
+
+```
+06-ourdigital-designer/
+├── code/
+│   ├── SKILL.md
+│   └── scripts/
+│       ├── generate_prompt.py
+│       └── mood_calibrator.py
+├── desktop/
+│   ├── SKILL.md
+│   └── skill.yaml
+├── shared/
+│   └── references/
+│       ├── visual-metaphors.md
+│       ├── color-palettes.md
+│       └── advanced-techniques.md
+├── docs/
+│   └── CHANGELOG.md
+└── README.md
+```
+
+## Visual Approach
+
+| Essay Type | Visual Strategy | Color Mood |
+|-----------|-----------------|------------|
+| Technology | Organic-digital hybrids | Cool blues → warm accents |
+| Social | Network patterns | Desaturated → hope spots |
+| Philosophy | Zen space | Monochrome + single accent |
+| Cultural | Layered traditions | Earth tones → modern hues |
+
+## Technical Specs
+
+| Field | Value |
+|-------|-------|
+| Dimensions | 1200x630px (OG standard) |
+| Style | Vector illustration + subtle textures |
+| Colors | 60-30-10 rule |
+| Format | WebP primary, JPG fallback |
+
+## Integration
+
+Works with:
+- `02-ourdigital-blog` - Korean blog images
+- `03-ourdigital-journal` - English essay images
+- `01-ourdigital-brand-guide` - Brand colors
+- MidJourney, DALL-E, Stable Diffusion
+
+## Version
+
+- Current: 1.1.0
+- Author: OurDigital