Add shadertoy-server example for WebGL shader rendering (#226)

Introduces a new MCP App example that renders ShaderToy-compatible GLSL
fragment shaders in real-time using WebGL 2.0 and ShaderToyLite.js.

Features:
- Standard ShaderToy uniforms (`iTime`, `iResolution`, `iMouse`, etc.)
- Multi-pass rendering with buffers A-D for feedback effects
- Shader compilation error overlay

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

examples/shadertoy-server/src/mcp-app.css

@@ -0,0 +1,12 @@
+html, body {
+  margin: 0;
+  width: 100%;
+  height: 100%;
+  overflow: hidden;
+}
+
+#canvas {
+  width: 100%;
+  height: 100%;
+  display: block;
+}