fix: include source files and TypeScript configs in npm package

- Add src/, tsconfig.*.json, and spec.types.ts to files array
- This enables postinstall builds when installed from GitHub fork
- Required for downstream packages to build the SDK during installation

Author: cameroncooke

package.json

@@ -32,7 +32,10 @@
     }
   },
   "files": [
-    "dist"
+    "dist",
+    "src",
+    "tsconfig.*.json",
+    "spec.types.ts"
   ],
   "scripts": {
     "fetch:spec-types": "curl -o spec.types.ts https://raw.githubusercontent.com/modelcontextprotocol/modelcontextprotocol/refs/heads/main/schema/draft/schema.ts",