feat(viz-platform): complete Sprint 1 - plugin structure and tests

Sprint 1 - viz-platform Plugin completed (13/13 issues):
- Commands: 7 files (initial-setup, chart, dashboard, theme, theme-new, theme-css, component)
- Agents: 3 files (theme-setup, layout-builder, component-check)
- Documentation: README.md, claude-md-integration.md
- Tests: 94 tests passing (68-99% coverage)
- CHANGELOG updated with completion status

Closes: #178, #179, #180, #181, #182

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

plugins/viz-platform/commands/theme.md

@@ -0,0 +1,69 @@
+---
+description: Apply an existing theme to the current context
+---
+
+# Apply Theme
+
+Apply an existing theme to activate its design tokens.
+
+## Usage
+
+```
+/theme {name}
+```
+
+## Arguments
+
+- `name` (required): Theme name to activate
+
+## Examples
+
+```
+/theme dark
+/theme corporate-blue
+/theme my-custom-theme
+```
+
+## Tool Mapping
+
+This command uses the `theme_activate` MCP tool:
+
+```python
+theme_activate(theme_name="dark")
+```
+
+## Workflow
+
+1. **User invokes**: `/theme dark`
+2. **Tool activates**: Theme becomes active for subsequent operations
+3. **Charts/layouts**: Automatically use active theme tokens
+
+## Built-in Themes
+
+| Theme | Description |
+|-------|-------------|
+| `light` | Mantine default light mode |
+| `dark` | Mantine default dark mode |
+
+## Listing Available Themes
+
+To see all available themes:
+
+```python
+theme_list()
+```
+
+Returns both built-in and custom themes.
+
+## Theme Effects
+
+When a theme is activated:
+- New charts inherit theme colors
+- New layouts use theme spacing
+- Components use theme typography
+- Callbacks can read active theme tokens
+
+## Related Commands
+
+- `/theme-new {name}` - Create a new theme
+- `/theme-css {name}` - Export theme as CSS