Use SDK imports for TypeScript and remote refs for JSON Schema

- schema.ts: Import core MCP types from @modelcontextprotocol/sdk/types.js
  instead of inline stubs
- schema.json: Use remote \ URIs pointing to core MCP schema at
  https://raw.githubusercontent.com/modelcontextprotocol/modelcontextprotocol/
  main/schema/2025-11-25/schema.json
- Add package.json with SDK and TypeScript as devDependencies
- Add .gitignore for node_modules
- Add skipLibCheck to tsconfig.json
- Add index signature to TaskStatusNotificationParams for SDK type compat

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tsconfig.json

@@ -4,7 +4,8 @@
     "noEmit": true,
     "target": "ES2020",
     "module": "ES2020",
-    "moduleResolution": "node"
+    "moduleResolution": "node",
+    "skipLibCheck": true
   },
   "include": ["schema/**/*.ts"]
 }