Code improvements

- [ ] Disable listeners/pollers when the browser is not focused
- [ ] Properly clean listeners when a field is disconnected (this somehow isn't creating problems now 🙏 but it should be fixed via `gt:kill`)

Start by tracing the listeners and pollers involved in browser focus handling, then inspect the field-disconnection lifecycle and the `gt:kill` event. Done means inactive browser tabs no longer keep those listeners or pollers running, and disconnected fields clean them up through `gt:kill`; the issue names no files or tests to run.

Written by the indexing model from the issue text.