terminal bell

### 🚀 The feature, motivation and pitch

It would be nice to optionally call the terminal bell when a pomo timer finishes. It looks like this is possible using the `on_open` hook in nvim-notify:

https://github.com/rcarriga/nvim-notify/issues/246

Start by reviewing the nvim-notify on_open hook and the linked nvim-notify issue #246. Trace where the pomo timer finishes and its notification is opened, then determine how an optional terminal bell should be configured and triggered. Done means the bell is opt-in and occurs when the timer finishes without changing default behavior.

Written by the indexing model from the issue text.