App 2.16.4: drop-downs that keep full screen

Back to drop-downs for upload frequency, tyre pressure unit and accent
colour, as Material exposed dropdown menus instead of Spinners. A
Spinner's list is a focusable window of its own without the
full-screen flags, so the car showed its bars while it was open; an
exposed dropdown's list leaves the focus with the activity, so the app
stays full screen. Styled like the other input fields, with full-height
rows. Replaces the buttons of 2.16.3.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QLJfZQZeAKAwSqViTmLzki

SPECS.md

@@ -112,8 +112,11 @@ tyre pressures, GPS (lat, lon, elevation, heading) and the is_* flags. It does *
   INGEST_TOKEN) into git and pushed it. Commit amended and force-pushed; both values regenerated in
   the now gitignored `k8s/secrets.yaml` (since moved to `k8s/secrets/secrets.yaml`, outside
   `kubectl apply -f k8s/`). Filled-in secrets live only there from now on.
+- 2026-10-18 — App 2.16.4: drop-downs again, as Material exposed dropdown menus: their list leaves
+  the focus with the activity, so full screen stays (a Spinner's list is a focusable window of its
+  own without the full-screen flags). 2.16.3 had replaced them with buttons.
 - 2026-10-18 — App 2.16.3: full screen stays while choosing or reading a dialog. Drop-downs (upload
-  frequency, tyre unit, accent colour) are now buttons on the page: a drop-down is a window of its
+  frequency, tyre unit, accent colour) became buttons on the page: a drop-down is a window of its
   own without the full-screen flags, so the car showed its bars while it was open. Dialogs are
   shown unfocusable, given the activity's full-screen flags, then allowed focus
   (`showKeepingFullScreen`); none of them takes typing.