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/layout-templates.md

@@ -0,0 +1,70 @@
+# Layout Templates
+
+## Available Templates
+
+### Basic
+Single-column layout with header and content area.
+```
++-----------------------------+
+|          Header             |
++-----------------------------+
+|                             |
+|          Content            |
+|                             |
++-----------------------------+
+```
+
+### Sidebar
+Layout with collapsible sidebar navigation.
+```
++--------+--------------------+
+|        |       Header       |
+|  Nav   +--------------------+
+|        |                    |
+|        |      Content       |
+|        |                    |
++--------+--------------------+
+```
+
+### Tabs
+Tabbed layout for multi-page dashboards.
+```
++-----------------------------+
+|          Header             |
++------+------+------+--------+
+| Tab1 | Tab2 | Tab3 |        |
++------+------+------+--------+
+|                             |
+|       Tab Content           |
+|                             |
++-----------------------------+
+```
+
+### Split
+Split-pane layout for comparisons.
+```
++-----------------------------+
+|          Header             |
++--------------+--------------+
+|              |              |
+|    Left      |    Right     |
+|    Pane      |    Pane      |
+|              |              |
++--------------+--------------+
+```
+
+## Filter Types
+
+Available filter components:
+- `dropdown` - Single/multi-select dropdown
+- `date_range` - Date range picker
+- `slider` - Numeric range slider
+- `checkbox` - Checkbox group
+- `search` - Text search input
+
+## Output
+
+Layout structures can be:
+- Used with page tools to create full app
+- Rendered as a Dash layout
+- Combined with chart components