Add accessibility report cookbook recipe

Add a new cookbook recipe that generates WCAG accessibility reports using
the Playwright MCP server. Includes streaming output, structured report
formatting, and optional Playwright test generation.

- C#, TypeScript, Python, and Go implementations
- Markdown documentation for each language
- Updated cookbook.yml, copilot-sdk README, and package.json

cookbook/copilot-sdk/nodejs/recipe/package.json

@@ -8,7 +8,8 @@
     "multiple-sessions": "tsx multiple-sessions.ts",
     "managing-local-files": "tsx managing-local-files.ts",
     "pr-visualization": "tsx pr-visualization.ts",
-    "persisting-sessions": "tsx persisting-sessions.ts"
+    "persisting-sessions": "tsx persisting-sessions.ts",
+    "accessibility-report": "tsx accessibility-report.ts"
   },
   "dependencies": {
     "@github/copilot-sdk": "*"