toggle switch does not show focus

### What went wrong?

The toggle switch (used for named entity view) does not show keyboard focus, making it difficult to use by keyboard.

See [WCAG criterion 2.4.7: focus must be visible](https://www.w3.org/TR/WCAG21/#focus-visible)

### What did you expect to happen?

See this description of the [switch pattern](https://www.w3.org/WAI/ARIA/apg/patterns/switch/) for some examples.

### Screenshot

Screen recording below. In the recording, I'm tabbing through the page and toggling the switch, but there is no indication when the keyboard focus moves to the switch.

[Screen recording of I-analyzer. Shows the user navigating by tabbing and operating the switch.](https://github.com/user-attachments/assets/49c5defa-0a3c-4c3b-a483-39b78b89a099)

### Where did you find the bug?

- [X] https://ianalyzer.hum.uu.nl
- [ ] https://peopleandparliament.hum.uu.nl
- [ ] https://peace.sites.uu.nl
- [ ] a server hosted elsewhere (i.e. not by the research software lab)
- [ ] a local server

### Version

5.14.1

### Steps to reproduce

Visit a document in a corpus with named entities, e.g. https://ianalyzer.hum.uu.nl/document/troonredes/1824_troonrede

Open the named-entity document at the provided iAnalyzer URL and reproduce the issue by tabbing to the toggle switch. Locate the switch implementation and its styling, then verify that keyboard focus is visibly indicated and retest the keyboard interaction against the linked WCAG and switch-pattern guidance.

Written by the indexing model from the issue text.