test(prefs): cover the automatic local clock's round trip and restore

Also reuse ZoneOffsetFormat.gmtLabel for the Etc/GMT names rather than
a second formatter, and bring the city-fallback docs up to date.

app/src/main/java/de/jeanlucmakiola/clockula/domain/worldclock/ZoneCatalog.kt

@@ -57,7 +57,8 @@ object ZoneCatalog {
 
     /**
      * The last `/`-segment with underscores replaced by spaces, trimmed; the
-     * input trimmed when that is blank. Never throws.
+     * input trimmed when that is blank. `Etc/GMT±n` is the exception: it is
+     * named by its real offset instead. Never throws.
      */
     fun cityFallbackFor(zoneId: String): String {
         etcOffsetName(zoneId)?.let { return it }
@@ -74,11 +75,12 @@ object ZoneCatalog {
     private fun etcOffsetName(zoneId: String): String? {
         val match = ETC_OFFSET.matchEntire(zoneId.trim()) ?: return null
         val hours = match.groupValues[2].toInt()
-        if (hours == 0) return "GMT"
-        val sign = if (match.groupValues[1] == "-") "+" else "-"
-        return "GMT$sign$hours"
+        val sign = if (match.groupValues[1] == "-") 1 else -1
+        return ZoneOffsetFormat.gmtLabel(sign * hours * MINUTES_PER_HOUR)
     }
 
+    private const val MINUTES_PER_HOUR = 60
+
     private val ETC_OFFSET = Regex("""Etc/GMT([+-])(\d{1,2})""")
 
     /** By `ZoneSearch.fold(city)` ascending, then [ZoneEntry.zoneId] ascending. */

app/src/main/java/de/jeanlucmakiola/clockula/ui/worldclock/WorldClockRowState.kt

@@ -18,7 +18,7 @@ import kotlin.time.toJavaInstant
 internal data class WorldClockRowState(
     val id: Long,
     val zoneId: String,
-    /** The user's label when set, else the ICU city, else the id's last segment. Never blank. */
+    /** The user's label when set, else the ICU city, else `ZoneCatalog.cityFallbackFor`. Never blank. */
     val name: String,
     /** Truncated to the minute. Non-null **exactly** when [known]. */
     val time: LocalTime?,

app/src/test/java/de/jeanlucmakiola/clockula/data/prefs/ClockPrefsTest.kt

@@ -53,6 +53,7 @@ class ClockPrefsTest {
         prefs.setTimerRingtoneUri("content://t")
         prefs.setDismissChallenge(DismissChallenge.HOLD)
         prefs.setHomeZoneId("Europe/Berlin")
+        prefs.setAutomaticLocalClock(false)
 
         assertThat(prefs.defaults.first()).isEqualTo(
             ClockDefaults(
@@ -64,6 +65,7 @@ class ClockPrefsTest {
                 timerRingtoneUri = "content://t",
                 dismissChallenge = DismissChallenge.HOLD,
                 homeZoneId = "Europe/Berlin",
+                automaticLocalClock = false,
             ),
         )
     }

app/src/test/java/de/jeanlucmakiola/clockula/data/prefs/SettingsPrefsTest.kt

@@ -74,7 +74,12 @@ class SettingsPrefsTest {
             BackupSettings(
                 themeMode = ThemeMode.DARK,
                 dynamicColor = false,
-                defaults = ClockDefaults(snoozeMinutes = 99, volumeRampSeconds = 99, alarmRingtoneUri = "  "),
+                defaults = ClockDefaults(
+                    snoozeMinutes = 99,
+                    volumeRampSeconds = 99,
+                    alarmRingtoneUri = "  ",
+                    automaticLocalClock = false,
+                ),
                 timerPresets = listOf(5.minutes, 1.minutes, 5.minutes),
             ),
         )
@@ -84,6 +89,7 @@ class SettingsPrefsTest {
         assertThat(prefs.currentDefaults().snoozeMinutes).isEqualTo(60)
         assertThat(prefs.currentDefaults().volumeRampSeconds).isEqualTo(60)
         assertThat(prefs.currentDefaults().alarmRingtoneUri).isNull()
+        assertThat(prefs.currentDefaults().automaticLocalClock).isFalse()
         assertThat(prefs.timerPresets.first()).containsExactly(1.minutes, 5.minutes).inOrder()
     }