refactor(viz-platform): extract skills and slim commands

Extract shared knowledge from 10 commands into 7 reusable skills:
- mcp-tools-reference.md: All viz-platform MCP tool signatures
- theming-system.md: Theme tokens, CSS variables, color palettes
- accessibility-rules.md: WCAG contrast, color-blind safe palettes
- dmc-components.md: DMC categories, validation, common props
- responsive-design.md: Breakpoints, mobile-first, grid config
- chart-types.md: Plotly chart types, export formats, resolution
- layout-templates.md: Dashboard templates, filter types

All commands now reference skills via "Skills to Load" section.
Commands reduced from 1396 lines total to 427 lines (69% reduction).

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

plugins/viz-platform/skills/theming-system.md

@@ -0,0 +1,104 @@
+# Theming System
+
+## Design Tokens
+
+Themes define design tokens for consistent styling across components.
+
+### Theme Properties
+
+| Category | Properties |
+|----------|------------|
+| Colors | `primary_color`, `color_scheme`, `colors` |
+| Typography | `font_family`, `heading_font_family` |
+| Spacing | `border_radius`, `spacing_scale` |
+
+### Color Scheme
+- `light` - Light background, dark text
+- `dark` - Dark background, light text
+
+### Border Radius Scale
+| Size | Value |
+|------|-------|
+| xs | 0.125rem |
+| sm | 0.25rem |
+| md | 0.5rem |
+| lg | 1rem |
+| xl | 2rem |
+
+## Mantine Color Palette
+
+Available primary colors:
+- blue, cyan, teal, green, lime
+- yellow, orange, red, pink, grape
+- violet, indigo, gray, dark
+
+Each color has 10 shades (0-9), where 5 is the primary shade.
+
+## Custom Color Definition
+
+```python
+colors={
+    "custom": [
+        "#e6f7ff",  # 0 - lightest
+        "#bae7ff",  # 1
+        "#91d5ff",  # 2
+        "#69c0ff",  # 3
+        "#40a9ff",  # 4
+        "#1890ff",  # 5 - primary
+        "#096dd9",  # 6
+        "#0050b3",  # 7
+        "#003a8c",  # 8
+        "#002766"   # 9 - darkest
+    ]
+}
+```
+
+## CSS Custom Properties
+
+Exported themes use Mantine CSS variable naming:
+
+```css
+:root {
+  /* Colors */
+  --mantine-color-scheme: light;
+  --mantine-primary-color: indigo;
+  --mantine-color-primary-0: #edf2ff;
+  --mantine-color-primary-5: #5c7cfa;
+  --mantine-color-primary-9: #364fc7;
+
+  /* Typography */
+  --mantine-font-family: Inter, sans-serif;
+  --mantine-font-size-xs: 0.75rem;
+  --mantine-font-size-md: 1rem;
+
+  /* Spacing */
+  --mantine-spacing-xs: 0.625rem;
+  --mantine-spacing-md: 1rem;
+
+  /* Border Radius */
+  --mantine-radius-sm: 0.25rem;
+  --mantine-radius-md: 0.5rem;
+
+  /* Shadows */
+  --mantine-shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.1);
+  --mantine-shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
+}
+```
+
+## Theme Inheritance
+
+Create themes based on existing ones:
+```python
+theme_extend(
+    base_theme="dark",
+    name="dark-corporate",
+    overrides={"primary_color": "indigo"}
+)
+```
+
+## Built-in Themes
+
+| Theme | Description |
+|-------|-------------|
+| `light` | Mantine default light mode |
+| `dark` | Mantine default dark mode |