core-time: add formatDateTimeCompact for dense list rows

Drops the year in the current year and drops the time when it carries no information (all-day items or a midnight time), so list rows show glanceable dates like "20 Jun" or "20 Jun · 14:30".

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

core-time/src/main/kotlin/de/jeanlucmakiola/floret/time/DateTimeFormat.kt

@@ -1,8 +1,13 @@
 package de.jeanlucmakiola.floret.time
 
+import java.time.LocalDate
+import java.time.LocalTime
 import java.time.ZoneId
+import java.time.chrono.IsoChronology
 import java.time.format.DateTimeFormatter
+import java.time.format.DateTimeFormatterBuilder
 import java.time.format.FormatStyle
+import java.util.Locale
 import kotlin.time.Instant
 
 /**
@@ -26,3 +31,28 @@ fun Instant.formatTime(): String = atSystemZone().format(timeFormatter)
 /** Date alone for all-day items, otherwise date + time. */
 fun Instant.formatDateTime(allDay: Boolean): String =
     if (allDay) formatDate() else "${formatDate()} · ${formatTime()}"
+
+// The locale's medium date pattern with the year token stripped, e.g. "20 Jun" /
+// "Jun 20" — derived from the pattern so day/month order still follows the locale.
+// Built once; locale changes within a running process are rare enough to ignore.
+private val dateNoYearFormatter: DateTimeFormatter = run {
+    val medium = DateTimeFormatterBuilder.getLocalizedDateTimePattern(
+        FormatStyle.MEDIUM, null, IsoChronology.INSTANCE, Locale.getDefault(),
+    )
+    val noYear = medium.replace(Regex("[\\s.,/'’-]*y+[\\s.,/'’-]*"), " ").trim()
+    DateTimeFormatter.ofPattern(noYear, Locale.getDefault())
+}
+
+/**
+ * Compact form for dense list rows: the year is dropped when the date is in the
+ * current year, and the time is dropped when it carries no information (all-day
+ * items, or a midnight time). Examples: "20 Jun", "20 Jun · 14:30", "20 Jun 2027".
+ */
+fun Instant.formatDateTimeCompact(allDay: Boolean): String {
+    val zdt = atSystemZone()
+    val datePart =
+        if (zdt.year == LocalDate.now(ZoneId.systemDefault()).year) zdt.format(dateNoYearFormatter)
+        else formatDate()
+    return if (allDay || zdt.toLocalTime() == LocalTime.MIDNIGHT) datePart
+    else "$datePart · ${formatTime()}"
+}