Switched the CDN provider for the AWS SDK (R2 client) to the bundled version from `esm.sh` (`?bundle`). This resolves a runtime error `[unenv] fs.readFile is not implemented yet!` which occurred because the previous build was attempting to import Node.js-specific credential providers that rely on the filesystem.
The bundled version from `esm.sh` correctly resolves the browser entry points and provides browser-compatible polyfills (or safe defaults) for dependencies, ensuring the SDK initializes correctly in the client environment.
This change updates the `AWS_SDK_SPECIFIER` constant in `js/storage/r2-s3.js`.