The `settings-utc-timestamps` checkbox sat inside the Token Spam Protection
well, immediately after the dust-threshold input. It is a display preference
and has nothing to do with spam filtering, so it now renders in the Display
well next to the theme selector.
Markup move only. The checkbox is wired by id — `$("settings-utc-timestamps")`
in `src/popup/views/settings.js`, where `$` is `document.getElementById` — for
both the initial `checked` assignment and the `change` handler, so nothing in
the wiring depends on the element's parent or siblings. `state.utcTimestamps`,
`saveState`/`loadState` and the `helpers.js` formatting path are untouched.
`tests/settingsUtcTimestamps.test.js` pins both halves down: the checkbox
appears exactly once and inside the Display well rather than the spam well,
and the setting still round-trips through storage.
