perf: stabilize clock width to prevent bar layout cascade

when clock text changed width (e.g. minute tick), the center section
shifted, causing all bargroups to recompute _posFrac and borderColor.
minText prevents the layout shift entirely.

modules/Clock.qml

@@ -10,5 +10,6 @@ M.BarLabel {
 
     font.pixelSize: M.Theme.fontSize + 1
     label: Qt.formatDateTime(clock.date, "ddd, dd. MMM  HH:mm")
+    minText: "Mi., 00. Sep.  00:00"
     tooltip: Qt.formatDateTime(clock.date, "dddd, dd. MMMM yyyy\nHH:mm:ss")
 }