feat(viz-platform): add /design-review command for design audits

Add standalone command that invokes the design-reviewer agent to
perform detailed design system compliance audits on target paths.
Returns comprehensive findings grouped by severity with file paths,
line numbers, and recommended fixes.

Closes #359

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

plugins/viz-platform/commands/design-review.md

@@ -0,0 +1,70 @@
+---
+description: Audit codebase for design system compliance
+arguments:
+  - name: path
+    description: File or directory to audit
+    required: true
+---
+
+# /design-review
+
+Scans target path for Dash Mantine Components usage and validates against design system standards.
+
+## Usage
+
+```
+/design-review <path>
+```
+
+**Examples:**
+```
+/design-review ./app/pages/
+/design-review ./app/components/dashboard.py
+/design-review .
+```
+
+## What It Does
+
+1. **Activates** the `design-reviewer` agent in review mode
+2. **Loads** the `skills/design-system-audit.md` skill
+3. **Scans** target path for:
+   - Python files with DMC imports
+   - Component instantiations and their props
+   - Style dictionaries and color values
+   - Accessibility attributes
+4. **Validates** against:
+   - DMC component registry (valid components and props)
+   - Theme token usage (no hardcoded colors/sizes)
+   - Accessibility standards (contrast, ARIA labels)
+5. **Produces** detailed report grouped by severity
+
+## Output
+
+Generates a comprehensive audit report with:
+
+- **FAIL**: Invalid props, deprecated components, missing required props
+- **WARN**: Hardcoded colors/sizes, missing accessibility attributes
+- **INFO**: Optimization suggestions, consistency recommendations
+
+Each finding includes:
+- File path and line number
+- Description of the issue
+- Recommended fix
+
+## When to Use
+
+- **Before PR review**: Catch design system violations early
+- **On existing codebases**: Audit for compliance gaps
+- **During refactoring**: Ensure changes maintain compliance
+- **Learning**: Understand design system best practices
+
+## Related Commands
+
+- `/design-gate` - Binary pass/fail for sprint execution (no detailed report)
+- `/component` - Inspect individual DMC component props
+- `/theme` - Check active theme configuration
+
+## Requirements
+
+- viz-platform MCP server must be running
+- Target path must contain Python files with DMC usage