dsh-bell-notify: Add configurable Agent lifecycle bell to DeepSeek Harness

`dsh-bell-notify` is a community plugin for DeepSeek Harness (`dsh`) designed to convert Agent lifecycle events into low-disturbance sound prompts, helping developers track task progress without constant page monitoring. Maintained by `Laplace-bit`, this plugin is open-source under the MIT license and is an unofficial release. Its core features include 10 configurable lifecycle event prompts, with "Start Execution", "Waiting for Confirmation", and "Round Completed" enabled by default. Each event supports previewing, uploading custom audio, and resetting to default. Audio is synthesized in real-time via the Web Audio API, is available offline, and data is stored solely in the browser (using `localStorage` and `IndexedDB`) without being uploaded to external servers. The plugin offers a master switch, volume control, and event settings.