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/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()))