Format the "updated" timestamp as a locale-aware date/time

Replaces the raw "2026-09-10 10:03:54" with each platform's own
locale-formatted, no-seconds rendering (e.g. "Sep 10, 2026, 10:03 AM"
in en-US) — mirroring how amounts are already locale-formatted
elsewhere (NumberFormat.kt). Android uses the pre-java.time
Calendar/DateFormat APIs since minSdk 24 predates java.time (API 26)
and the project has no core library desugaring configured.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FXcrACM5sok3M1KQJ8kByy

shared/src/androidMain/kotlin/xyz/tyiu/satsprice/domain/DateFormat.android.kt

@@ -0,0 +1,17 @@
+package xyz.tyiu.satsprice.domain
+
+import kotlinx.datetime.LocalDateTime
+import java.text.DateFormat
+import java.util.Calendar
+import java.util.Locale
+
+// java.time requires API 26+ (this app's minSdk is 24) without core library desugaring, so this
+// uses the older Calendar/DateFormat APIs instead, same as pre-java.time Android code always did.
+actual fun localizedDateTime(dateTime: LocalDateTime): String {
+    val calendar = Calendar.getInstance().apply {
+        clear()
+        set(dateTime.year, dateTime.monthNumber - 1, dateTime.dayOfMonth, dateTime.hour, dateTime.minute)
+    }
+    val formatter = DateFormat.getDateTimeInstance(DateFormat.MEDIUM, DateFormat.SHORT, Locale.getDefault())
+    return formatter.format(calendar.time)
+}

shared/src/appleMain/kotlin/xyz/tyiu/satsprice/domain/DateFormat.apple.kt

@@ -0,0 +1,27 @@
+package xyz.tyiu.satsprice.domain
+
+import kotlinx.datetime.LocalDateTime
+import platform.Foundation.NSCalendar
+import platform.Foundation.NSDateComponents
+import platform.Foundation.NSDateFormatter
+import platform.Foundation.NSDateFormatterMediumStyle
+import platform.Foundation.NSDateFormatterShortStyle
+import platform.Foundation.NSLocale
+import platform.Foundation.currentLocale
+
+actual fun localizedDateTime(dateTime: LocalDateTime): String {
+    val components = NSDateComponents().apply {
+        year = dateTime.year.toLong()
+        month = dateTime.monthNumber.toLong()
+        day = dateTime.dayOfMonth.toLong()
+        hour = dateTime.hour.toLong()
+        minute = dateTime.minute.toLong()
+    }
+    val date = NSCalendar.currentCalendar.dateFromComponents(components) ?: return dateTime.toString()
+    val formatter = NSDateFormatter().apply {
+        dateStyle = NSDateFormatterMediumStyle
+        timeStyle = NSDateFormatterShortStyle
+        locale = NSLocale.currentLocale
+    }
+    return formatter.stringFromDate(date)
+}

shared/src/commonMain/kotlin/xyz/tyiu/satsprice/domain/DateFormat.kt

@@ -0,0 +1,11 @@
+package xyz.tyiu.satsprice.domain
+
+import kotlinx.datetime.LocalDateTime
+
+/**
+ * A locale-aware, human-readable rendering of [dateTime] (e.g. "Sep 10, 2026, 10:03 AM" in
+ * en-US), using each platform's own date/time formatter — mirroring how [localizedGroupedInteger]
+ * and [localizedDecimalSeparator] format numbers. Deliberately drops seconds: a "last updated"
+ * label doesn't need second-level precision.
+ */
+expect fun localizedDateTime(dateTime: LocalDateTime): String

shared/src/commonMain/kotlin/xyz/tyiu/satsprice/ui/ConverterUiStateDisplay.kt

@@ -5,6 +5,7 @@ import kotlinx.datetime.toLocalDateTime
 import xyz.tyiu.satsprice.CurrencyInfo
 import xyz.tyiu.satsprice.domain.CurrencyConverter
 import xyz.tyiu.satsprice.domain.formatAmount
+import xyz.tyiu.satsprice.domain.localizedDateTime
 import xyz.tyiu.satsprice.domain.toBigDecimalOrNull
 import kotlin.time.Instant
 
@@ -52,7 +53,5 @@ fun ConverterUiState.unselectedCurrencies(): List<CurrencyInfo> =
 /** Whether the active price source quotes a rate for [code] — every currency is listed regardless. */
 fun ConverterUiState.isPriced(code: String): Boolean = code in pricedCurrencyCodes
 
-private fun Instant.toDateTimeString(): String {
-    val local = toLocalDateTime(TimeZone.currentSystemDefault())
-    return local.toString().substringBefore('.').replace('T', ' ')
-}
+private fun Instant.toDateTimeString(): String =
+    localizedDateTime(toLocalDateTime(TimeZone.currentSystemDefault()))

shared/src/jvmMain/kotlin/xyz/tyiu/satsprice/domain/DateFormat.jvm.kt

@@ -0,0 +1,13 @@
+package xyz.tyiu.satsprice.domain
+
+import kotlinx.datetime.LocalDateTime
+import kotlinx.datetime.toJavaLocalDateTime
+import java.time.format.DateTimeFormatter
+import java.time.format.FormatStyle
+import java.util.Locale
+
+actual fun localizedDateTime(dateTime: LocalDateTime): String {
+    val formatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM, FormatStyle.SHORT)
+        .withLocale(Locale.getDefault())
+    return dateTime.toJavaLocalDateTime().format(formatter)
+}

shared/src/webMain/kotlin/xyz/tyiu/satsprice/domain/DateFormat.web.kt

@@ -0,0 +1,16 @@
+package xyz.tyiu.satsprice.domain
+
+import kotlinx.datetime.LocalDateTime
+
+// Individual Int fields (rather than the LocalDateTime itself) cross the js() boundary, matching
+// the rest of this file's web interop — see SystemCurrencies.web.kt for why.
+private fun jsFormatDateTime(year: Int, month: Int, day: Int, hour: Int, minute: Int): String = js(
+    """(function() {
+        var date = new Date(year, month - 1, day, hour, minute);
+        var fmt = new Intl.DateTimeFormat(undefined, { dateStyle: 'medium', timeStyle: 'short' });
+        return fmt.format(date);
+    })()""",
+)
+
+actual fun localizedDateTime(dateTime: LocalDateTime): String =
+    jsFormatDateTime(dateTime.year, dateTime.monthNumber, dateTime.dayOfMonth, dateTime.hour, dateTime.minute)