feat(shadertoy): add streaming partial input, visibility optimization, host styling

Shadertoy server improvements:
- Add ontoolinputpartial handler to show code preview during generation
- Add IntersectionObserver to pause/play shader based on visibility
- Apply host style variables (theme, colors, fonts)
- Add border-radius with fullscreen mode support
- Use gradient background and ghost text color for code preview

Skill documentation updates:
- Add streaming partial input section with use cases
- Add visibility-based resource management pattern
- Add fullscreen mode API and CSS patterns
- Expand host styling with CSS variable usage examples

examples/shadertoy-server/mcp-app.html

@@ -9,6 +9,7 @@
 <body>
   <main class="main">
     <canvas id="canvas"></canvas>
+    <pre id="code-preview"></pre>
     <button id="fullscreen-btn" class="fullscreen-btn" title="Toggle fullscreen">
       <svg class="expand-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
         <path d="M8 3H5a2 2 0 0 0-2 2v3m18 0V5a2 2 0 0 0-2-2h-3m0 18h3a2 2 0 0 0 2-2v-3M3 16v3a2 2 0 0 0 2 2h3"/>