feat: default workout distance unit to the phone's measurement system

Read the phone's measurement preference (Android 14+ Regional preferences
override via the locale's -u-ms- extension, else ICU's locale-derived
US/UK = miles) and default the New Workout composer's km/mi selector to it.
Health Connect distances (always metres) are converted into the chosen unit on
pre-fill instead of being forced to km.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015qgqQKHSewRHVM8vSCLt9P

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/workouts/MeasurementSystem.kt

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.ui.screen.loggedIn.workouts
+
+import android.icu.util.LocaleData
+import android.icu.util.ULocale
+import java.util.Locale
+
+/**
+ * Whether the phone's measurement preference favours miles for distance.
+ *
+ * Honours the Android 14+ "Regional preferences → Measurement system" override,
+ * which the platform surfaces through the default locale's Unicode `-u-ms-`
+ * extension (`metric` / `ussystem` / `uksystem`). When no explicit override is
+ * set it falls back to ICU's locale-derived measurement system (US and UK both
+ * use miles for distance), available since API 24.
+ */
+fun phonePrefersMiles(): Boolean {
+    val locale = Locale.getDefault(Locale.Category.FORMAT)
+
+    locale.getUnicodeLocaleType("ms")?.let { ms ->
+        return ms == "ussystem" || ms == "uksystem"
+    }
+
+    return when (LocaleData.getMeasurementSystem(ULocale.forLocale(locale))) {
+        LocaleData.MeasurementSystem.US, LocaleData.MeasurementSystem.UK -> true
+        else -> false
+    }
+}

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/workouts/NewWorkoutViewModel.kt

@@ -54,7 +54,7 @@ class NewWorkoutViewModel : ViewModel() {
     var minutes by mutableStateOf("")
     var seconds by mutableStateOf("")
     var distance by mutableStateOf("")
-    var distanceUnit by mutableStateOf(DistanceTag.KILOMETERS)
+    var distanceUnit by mutableStateOf(if (phonePrefersMiles()) DistanceTag.MILES else DistanceTag.KILOMETERS)
     var calories by mutableStateOf("")
     var notes by mutableStateOf("")
 
@@ -100,8 +100,10 @@ class NewWorkoutViewModel : ViewModel() {
             seconds = (route.durationSeconds % 60).toString()
         }
         if (route.distanceMeters > 0) {
-            distance = ((route.distanceMeters / 1000.0 * 100).roundToInt() / 100.0).toString()
-            distanceUnit = DistanceTag.KILOMETERS
+            val miles = phonePrefersMiles()
+            distanceUnit = if (miles) DistanceTag.MILES else DistanceTag.KILOMETERS
+            val value = if (miles) route.distanceMeters / DistanceTag.METERS_PER_MILE else route.distanceMeters / 1000.0
+            distance = ((value * 100).roundToInt() / 100.0).toString()
         }
         if (route.calories > 0) calories = route.calories.toString()
 
@@ -127,7 +129,7 @@ class NewWorkoutViewModel : ViewModel() {
         minutes = ""
         seconds = ""
         distance = ""
-        distanceUnit = DistanceTag.KILOMETERS
+        distanceUnit = if (phonePrefersMiles()) DistanceTag.MILES else DistanceTag.KILOMETERS
         calories = ""
         notes = ""
         source = SourceTag.MANUAL