canvas-generate: AI-Orchestrated Canvas Generation

The flagship command. Takes a high-level description and produces a complete, populated canvas.

Read ../canvas/references/template-catalog.md for archetype descriptions. Read ../canvas/references/media-guide.md for image/SVG/GIF integration. Read ../canvas/references/mermaid-patterns.md for native diagram options. Read ../canvas/references/performance-guide.md for node limits.

Pipeline

User: "/canvas generate [description]"
          │
          ▼
   1. Analyze description
          │