feat(baoyu-image-cards): add image card series skill migrated from baoyu-xhs-images

Rename baoyu-xhs-images to baoyu-image-cards to decouple from Xiaohongshu platform.
Deprecate baoyu-xhs-images with migration notice pointing to baoyu-image-cards.

skills/baoyu-image-cards/references/elements/canvas.md

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+# Canvas & Layout
+
+Core canvas specifications and layout grids for Xiaohongshu infographics.
+
+## Aspect Ratios
+
+| Name | Ratio | Pixels | Note |
+|------|-------|--------|------|
+| portrait-3-4 | 3:4 | 1242×1660 | Highest traffic on XHS (recommended) |
+| square | 1:1 | 1242×1242 | Second recommended |
+| portrait-2-3 | 2:3 | 1242×1863 | Taller format |
+
+**Default**: portrait-3-4 for maximum engagement.
+
+## Safe Zones
+
+Avoid placing critical content in these areas:
+
+| Zone | Position | Reason |
+|------|----------|--------|
+| bottom-overlay | Bottom 10% | Title bar overlay on mobile |
+| top-right | Top-right corner | Like/share button overlay |
+| bottom-right | Bottom-right corner | Watermark position |
+
+```
+┌─────────────────────────────┐
+│                 [like/share]│  ← top-right: avoid
+│                             │
+│                             │
+│      ✓ SAFE CONTENT AREA    │
+│                             │
+│                             │
+│  [title bar overlay area]   │  ← bottom 10%: avoid key info
+└─────────────────────────────┘
+```
+
+## Grid Layouts
+
+### Density-Based Layouts
+
+| Layout | Info Density | Whitespace | Points/Image | Best For |
+|--------|--------------|------------|--------------|----------|
+| sparse | Low | 60-70% | 1-2 | Covers, quotes, impactful statements |
+| balanced | Medium | 40-50% | 3-4 | Standard content, tutorials |
+| dense | High | 20-30% | 5-8 | Knowledge cards, cheat sheets |
+
+### Structure-Based Layouts
+
+| Layout | Structure | Items | Best For |
+|--------|-----------|-------|----------|
+| list | Vertical enumeration | 4-7 | Rankings, checklists, step guides |
+| comparison | Left vs Right | 2 sections | Before/after, pros/cons |
+| flow | Connected nodes | 3-6 steps | Processes, timelines, workflows |
+| mindmap | Center radial | 4-8 branches | Concept maps, brainstorming, topic overview |
+| quadrant | 4-section grid | 4 sections | SWOT analysis, priority matrix, classification |
+
+## Layout by Position
+
+| Position | Recommended Layout | Why |
+|----------|-------------------|-----|
+| Cover | sparse | Maximum visual impact, clear title |
+| Setup | balanced | Context without overwhelming |
+| Core | balanced/dense/list | Based on content density |
+| Payoff | balanced/list | Clear takeaways |
+| Ending | sparse | Clean CTA, memorable close |
+
+## Grid Cells
+
+For multi-element compositions:
+
+| Name | Cells | Use Case |
+|------|-------|----------|
+| single | 1 | Hero image, maximum impact |
+| dual | 2 | Before/after, comparison |
+| triptych | 3 | Steps, process flow |
+| quad | 4 | Product showcase |
+| six-grid | 6 | Checklist, collection |
+| nine-grid | 9 | Multi-image gallery |
+
+## Visual Balance
+
+### Sparse Layout
+- Single focal point centered
+- Breathing room on all sides
+- Symmetrical composition
+
+### Balanced Layout
+- Top-weighted title
+- Evenly distributed content below
+- Clear visual hierarchy
+
+### Dense Layout
+- Organized grid structure
+- Clear section boundaries
+- Compact but readable spacing
+
+### List Layout
+- Left-aligned items
+- Clear number/bullet hierarchy
+- Consistent item format
+
+### Comparison Layout
+- Symmetrical left/right
+- Clear visual contrast
+- Divider between sections
+
+### Flow Layout
+- Directional flow (top→bottom or left→right)
+- Connected nodes with arrows
+- Clear progression indicators
+
+### Mindmap Layout
+- Central topic node
+- Radial branches outward
+- Hierarchical sub-branches
+- Organic curved connections
+
+### Quadrant Layout
+- 4-section grid (2×2)
+- Clear axis labels
+- Each quadrant with distinct content
+- Optional circular variant for cycles