[listen] Fixes api doc example directive

[chunhtai]

as title

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[gemini-code-assist]

Code Review

This pull request updates the version of the listen package to 1.0.0-beta.2 in pubspec.yaml and CHANGELOG.md. It also corrects the Dart doc example directives in packages/listen/lib/src/listen.dart by adding a leading slash to the example file paths. There are no review comments, and I have no feedback to provide.