gui: set minimum window size for KDE tiling

Add minimumWidth: 320 and minimumHeight: 240 to allow the window to
resize properly when tiled by KDE's window manager. Without explicit
minimums, Qt calculates implicit minimums from content that may be
too large for narrow tile slots.

kde/gui/main.qml

@@ -7,6 +7,8 @@ ApplicationWindow {
     visible: true
     width: 1000
     height: 600
+    minimumWidth: 320
+    minimumHeight: 240
     title: "Ollie"
     font.family: theme.fontFamily || Qt.application.font.family
     font.pointSize: theme.fontSize > 0 ? theme.fontSize : Qt.application.font.pointSize