Add client-side validation for tool output schemas

- Cache tool output schemas when listing tools
- Validate structuredContent against outputSchema during callTool
- Enforce that tools with outputSchema must return structuredContent
- Add json-schema-to-zod dependency for schema conversion
- Add comprehensive tests for validation scenarios

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

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

package.json

@@ -52,6 +52,7 @@
     "eventsource": "^3.0.2",
     "express": "^5.0.1",
     "express-rate-limit": "^7.5.0",
+    "json-schema-to-zod": "^2.6.1",
     "pkce-challenge": "^5.0.0",
     "raw-body": "^3.0.0",
     "zod": "^3.23.8",