feat(shadertoy): add fullscreen support + ditch insets for max visual effect (#278)

* feat(shadertoy): add fullscreen support

Add fullscreen toggle button that appears when the host supports fullscreen
display mode. Uses the same pattern as pdf-server:
- Check availableDisplayModes in host context
- Show/hide button based on capability
- Toggle between inline and fullscreen via requestDisplayMode()
- Update UI state on host context changes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* fix(shadertoy): button visibility after exiting fullscreen + Escape key

- Only update button visibility when availableDisplayModes is present
  in context (partial updates don't include all fields)
- Add Escape key handler to exit fullscreen mode

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

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

examples/shadertoy-server/package.json

@@ -17,7 +17,9 @@
     "build": "tsc --noEmit && cross-env INPUT=mcp-app.html vite build && tsc -p tsconfig.server.json && bun build server.ts --outdir dist --target node && bun build main.ts --outfile dist/index.js --target node --external \"./server.js\" --banner \"#!/usr/bin/env node\"",
     "watch": "cross-env INPUT=mcp-app.html vite build --watch",
     "serve": "bun --watch main.ts",
+    "serve:stdio": "bun main.ts --stdio",
     "start": "cross-env NODE_ENV=development npm run build && npm run serve",
+    "start:stdio": "cross-env NODE_ENV=development npm run build && npm run serve:stdio",
     "dev": "cross-env NODE_ENV=development concurrently 'npm run watch' 'npm run serve'",
     "prepublishOnly": "npm run build"
   },