refactor: rename command files for namespace consistency

BREAKING CHANGE: All generic command names now prefixed with plugin namespace.
See CHANGELOG.md v7.0.0 for complete rename map.

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

plugins/viz-platform/commands/viz-theme-css.md

@@ -0,0 +1,42 @@
+---
+description: Export a theme as CSS custom properties
+---
+
+# Export Theme as CSS
+
+## Skills to Load
+- skills/mcp-tools-reference.md
+- skills/theming-system.md
+
+## Visual Output
+
+```
++------------------------------------------------------------------+
+|  VIZ-PLATFORM - Theme CSS Export                                 |
++------------------------------------------------------------------+
+```
+
+Export a theme's design tokens as CSS custom properties.
+
+## Usage
+
+```
+/theme-css {name}
+```
+
+## Arguments
+
+- `name` (required): Theme name to export
+
+## Tool Mapping
+
+```python
+theme_export_css(theme_name="corporate")
+```
+
+Use cases: external CSS, design handoff, documentation, other frameworks.
+
+## Related Commands
+
+- `/theme {name}` - Apply a theme
+- `/theme-new {name}` - Create a new theme