Add paint-server example

[antonpk1]

Simple MCP App example: minimalistic drawing canvas with color picker.

What it does

• Opens a drawing canvas via the draw tool
• User picks colors and draws freehand
• Drawing is debounced (1s) and sent as a PNG image via updateModelContext
• Model can then describe what the user drew

Implementation

• Based on basic-server-vanillajs template
• Vanilla JS, no React
• Canvas scales export to max 256px (longest side)
• Uses pointer events for mouse + touch support

Testing

1. Add to Claude Desktop config:

"paint": {
  "command": "node",
  "args": ["path/to/ext-apps/examples/paint-server/dist/index.js", "--stdio"]
}

2. Ask Claude to draw
3. Draw something on the canvas
4. Ask Claude "what did I draw?"