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/README.md

@@ -0,0 +1,132 @@
+# Example: ShaderToy Server
+
+A demo MCP App that renders [ShaderToy](https://www.shadertoy.com/)-compatible GLSL fragment shaders in real-time using WebGL 2.0 and [ShaderToyLite.js](https://github.com/nickoala/ShaderToyLite).
+
+<table>
+  <tr>
+    <td><a href="https://modelcontextprotocol.github.io/ext-apps/screenshots/shadertoy-server/01-gradient.png"><img src="https://modelcontextprotocol.github.io/ext-apps/screenshots/shadertoy-server/01-gradient.png" alt="Gradient" width="100%"></a></td>
+    <td><a href="https://modelcontextprotocol.github.io/ext-apps/screenshots/shadertoy-server/02-kaleidoscope.png"><img src="https://modelcontextprotocol.github.io/ext-apps/screenshots/shadertoy-server/02-kaleidoscope.png" alt="Kaleidoscope" width="100%"></a></td>
+    <td><a href="https://modelcontextprotocol.github.io/ext-apps/screenshots/shadertoy-server/03-fractal.png"><img src="https://modelcontextprotocol.github.io/ext-apps/screenshots/shadertoy-server/03-fractal.png" alt="Kaleidoscope" width="100%"></a></td>
+  </tr>
+</table>
+
+## Features
+
+- **Real-time Rendering**: Renders GLSL shaders using WebGL 2.0
+- **ShaderToy Compatibility**: Uses the standard `mainImage(out vec4 fragColor, in vec2 fragCoord)` entry point
+- **Multi-pass Rendering**: Supports buffers A-D for feedback effects, blur chains, and simulations
+- **Standard Uniforms**: iResolution, iTime, iTimeDelta, iFrame, iMouse, iDate, iChannel0-3
+
+## Running
+
+1. Install dependencies:
+
+   ```bash
+   npm install
+   ```
+
+2. Build and start the server:
+
+   ```bash
+   npm run start:http  # for Streamable HTTP transport
+   # OR
+   npm run start:stdio  # for stdio transport
+   ```
+
+3. View using the [`basic-host`](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/basic-host) example or another MCP Apps-compatible host.
+
+### Tool Input Examples
+
+**Gradient with Time:**
+
+```glsl
+void mainImage(out vec4 fragColor, in vec2 fragCoord) {
+    vec2 uv = fragCoord / iResolution.xy;
+    fragColor = vec4(uv, 0.5 + 0.5*sin(iTime), 1.0);
+}
+```
+
+_Tool input:_
+
+```json
+{
+  "fragmentShader": "void mainImage(out vec4 fragColor, in vec2 fragCoord) {\n    vec2 uv = fragCoord / iResolution.xy;\n    fragColor = vec4(uv, 0.5 + 0.5*sin(iTime), 1.0);\n}"
+}
+```
+
+**Kaleidoscope**:
+
+```glsl
+void mainImage(out vec4 fragColor, in vec2 fragCoord) {
+    vec2 uv = (fragCoord - 0.5 * iResolution.xy) / iResolution.y;
+    float segments = 6.0;
+    float zoom = 1.0 + 0.3 * sin(iTime * 0.2);
+    float angle = atan(uv.y, uv.x) + iTime * 0.3;
+    float r = length(uv) * zoom;
+    angle = mod(angle, 6.28 / segments);
+    angle = abs(angle - 3.14 / segments);
+    vec2 p = vec2(cos(angle), sin(angle)) * r;
+    p += iTime * 0.1;
+    float v = sin(p.x * 10.0) * sin(p.y * 10.0);
+    v += sin(length(p) * 15.0 - iTime * 2.0);
+    v += sin(p.x * 5.0 + p.y * 7.0 + iTime);
+    vec3 col = 0.5 + 0.5 * cos(v * 2.0 + vec3(0.0, 2.0, 4.0) + iTime);
+    fragColor = vec4(col, 1.0);
+}
+```
+
+_Tool input:_
+
+```json
+{
+  "fragmentShader": "void mainImage(out vec4 fragColor, in vec2 fragCoord) {\n    vec2 uv = (fragCoord - 0.5 * iResolution.xy) / iResolution.y;\n    float segments = 6.0;\n    float zoom = 1.0 + 0.3 * sin(iTime * 0.2);\n    float angle = atan(uv.y, uv.x) + iTime * 0.3;\n    float r = length(uv) * zoom;\n    angle = mod(angle, 6.28 / segments);\n    angle = abs(angle - 3.14 / segments);\n    vec2 p = vec2(cos(angle), sin(angle)) * r;\n    p += iTime * 0.1;\n    float v = sin(p.x * 10.0) * sin(p.y * 10.0);\n    v += sin(length(p) * 15.0 - iTime * 2.0);\n    v += sin(p.x * 5.0 + p.y * 7.0 + iTime);\n    vec3 col = 0.5 + 0.5 * cos(v * 2.0 + vec3(0.0, 2.0, 4.0) + iTime);\n    fragColor = vec4(col, 1.0);\n}"
+}
+```
+
+**Interactive Julia Set** (mouse controls the fractal's c parameter):
+
+```glsl
+void mainImage(out vec4 fragColor, in vec2 fragCoord) {
+    vec2 uv = (fragCoord - 0.5 * iResolution.xy) / iResolution.y * 2.5;
+    vec2 mouse = (iMouse.xy / iResolution.xy - 0.5) * 2.0;
+    vec2 c = mouse;
+    vec2 z = uv;
+    float iter = 0.0;
+    for (int i = 0; i < 100; i++) {
+        z = vec2(z.x * z.x - z.y * z.y, 2.0 * z.x * z.y) + c;
+        if (dot(z, z) > 4.0) break;
+        iter++;
+    }
+    float t = iter / 100.0;
+    vec3 col = 0.5 + 0.5 * cos(3.0 + t * 6.28 * 2.0 + vec3(0.0, 0.6, 1.0));
+    if (iter == 100.0) col = vec3(0.0);
+    fragColor = vec4(col, 1.0);
+}
+```
+
+_Tool input:_
+
+```json
+{
+  "fragmentShader": "void mainImage(out vec4 fragColor, in vec2 fragCoord) {\n    vec2 uv = (fragCoord - 0.5 * iResolution.xy) / iResolution.y * 2.5;\n    vec2 mouse = (iMouse.xy / iResolution.xy - 0.5) * 2.0;\n    vec2 c = mouse;\n    vec2 z = uv;\n    float iter = 0.0;\n    for (int i = 0; i < 100; i++) {\n        z = vec2(z.x * z.x - z.y * z.y, 2.0 * z.x * z.y) + c;\n        if (dot(z, z) > 4.0) break;\n        iter++;\n    }\n    float t = iter / 100.0;\n    vec3 col = 0.5 + 0.5 * cos(3.0 + t * 6.28 * 2.0 + vec3(0.0, 0.6, 1.0));\n    if (iter == 100.0) col = vec3(0.0);\n    fragColor = vec4(col, 1.0);\n}"
+}
+```
+
+## Architecture
+
+### Server (`server.ts`)
+
+Exposes a single `render-shadertoy` tool that accepts:
+
+- `fragmentShader`: Main Image shader code (required)
+- `common`: Shared code across all shaders (optional)
+- `bufferA`: Buffer A shader, accessible as iChannel0 (optional)
+- `bufferB`: Buffer B shader, accessible as iChannel1 (optional)
+- `bufferC`: Buffer C shader, accessible as iChannel2 (optional)
+- `bufferD`: Buffer D shader, accessible as iChannel3 (optional)
+
+### App (`src/mcp-app.ts`)
+
+- Receives shader code via `ontoolinput` handler
+- Uses ShaderToyLite.js for WebGL rendering
+- Displays compilation errors in an overlay