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>

package.json

@@ -0,0 +1,14 @@
+{
+  "name": "@modelcontextprotocol/experimental-ext-tasks",
+  "private": true,
+  "version": "0.1.0",
+  "description": "MCP Tasks Extension - Experimental extension for task management in the Model Context Protocol",
+  "license": "Apache-2.0",
+  "scripts": {
+    "check:schema": "tsc --noEmit"
+  },
+  "devDependencies": {
+    "@modelcontextprotocol/sdk": "^1.29.0",
+    "typescript": "^5.0.0"
+  }
+}