canvas-create: Create New Canvases

Operations

Blank Canvas (/canvas create [name])

1. Slugify the name: lowercase, spaces to hyphens, strip special chars.
2. Determine canvas directory (see canvas orchestrator for context detection).
3. Create [canvas_dir]/[slug].canvas with starter structure:

{
  "nodes": [
    {
      "id": "zone-default",
      "type": "group",
      "label": "General",