feat: relative or absolute timestamping depending on time/date proximity

- implement LocaleUtils.formatRelativeTimestamp() that does all the heavy
  lifting
- use it in StatusTimeStampLabel -> propagates to all message timestamps
  (chat, activity center, settings, etc)

Closes #9397

ui/StatusQ/src/StatusQ/Components/private/statusMessage/StatusTimeStampLabel.qml

@@ -12,7 +12,7 @@ StatusBaseText {
     color: Theme.palette.baseColor1
     font.pixelSize: 10
     visible: !!text
-    text: showFullTimestamp ? LocaleUtils.formatDateTime(timestamp) : LocaleUtils.formatTime(timestamp, Locale.ShortFormat)
+    text: showFullTimestamp ? LocaleUtils.formatDateTime(timestamp) : LocaleUtils.formatRelativeTimestamp(timestamp)
     StatusToolTip {
         id: tooltip
         visible: hhandler.hovered && !!text

ui/StatusQ/src/StatusQ/Core/LocaleUtils.qml

@@ -78,6 +78,8 @@ QtObject {
 
         readonly property var amPmFormatChars: ["AP", "A", "ap", "a"]
 
+        readonly property int msInADay: 86400000
+
         // try to parse date from a number or ISO string timestamp
         function readDate(value) {
             if (typeof value === "undefined") // default to "now" if omitted
@@ -102,6 +104,13 @@ QtObject {
                 return result
             }
         }
+
+        // return full days between 2 dates
+        function daysBetween(firstDate, secondDate) {
+            firstDate.setHours(0, 0, 0) // discard time
+            secondDate.setHours(0, 0, 0)
+            return Math.round(Math.abs((firstDate - secondDate) / d.msInADay)) // Math.round: not all days are 24 hours long!
+        }
     }
 
     readonly property Settings settings: Settings {
@@ -162,6 +171,34 @@ QtObject {
         return value.toLocaleString(loc, formatString)
     }
 
+    // TODO use JS Intl.RelativeTimeFormat in Qt 6?
+    function formatRelativeTimestamp(timestamp) {
+        const now = new Date()
+        const value = d.readDate(timestamp)
+        const loc = Qt.locale()
+        const formatString = d.fixupTimeFormatString(loc.timeFormat(Locale.ShortFormat)) // format string for the time part
+        const dayDifference = d.daysBetween(d.readDate(timestamp), now)
+
+        // within last day, 2 or 7 days
+        if (dayDifference < 1) // today -> "Today 14:23"
+            return qsTr("Today %1").arg(value.toLocaleTimeString(loc, formatString))
+
+        if (dayDifference < 2) // yesterday -> "Yesterday 14:23"
+            return qsTr("Yesterday %1").arg(value.toLocaleTimeString(loc, formatString))
+
+        if (dayDifference < 7) // last 7 days -> "Mon 14:23"
+            return qsTr("%1 %2").arg(loc.standaloneDayName(value.getDay(), Locale.ShortFormat)).arg(value.toLocaleTimeString(loc, formatString))
+
+        // otherwise
+        var fullFormatString = d.fixupTimeFormatString(loc.dateTimeFormat(Locale.ShortFormat))
+        if (now.getFullYear() === value.getFullYear())
+            fullFormatString = fullFormatString.replace(/y/g, "") // strip year part, if current year -> "31 December 09:41"
+        else
+            fullFormatString = fullFormatString.replace("yy", "yyyy") // different year -> "31 December 2022 09:41"
+
+        return value.toLocaleString(loc, fullFormatString)
+    }
+
     function getTimeDifference(d1, d2) {
         const day1Year = d1.getFullYear()
         const day1Month = d1.getMonth()