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/global.css

@@ -0,0 +1,12 @@
+* {
+  box-sizing: border-box;
+}
+
+html, body {
+  font-family: system-ui, -apple-system, sans-serif;
+  font-size: 1rem;
+}
+
+code {
+  font-size: 1em;
+}