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

app/build.gradle

@@ -34,8 +34,8 @@ android {
         applicationId "com.stinnesbeck.nilsmg4"
         minSdk 27
         targetSdk 36
-        versionCode 87
-        versionName "2.16.3"
+        versionCode 88
+        versionName "2.16.4"
 
         // Nothing about the server ships in the APK: its URL and ingest token are entered in
         // the app's Server tab (ServerConfig), and the database is only reachable by the server.