fix: --dp-menu-min-width not propagated to month-picker mode (fixes #954)

Author: Jasenkoo

src/VueDatePicker/components/Common/SelectionOverlay.vue

@@ -174,7 +174,7 @@
     );
 
     const dpOverlayStyle = computed(() =>
-        props.useRelative ? { height: `${props.height}px`, width: `${260}px` } : undefined,
+        props.useRelative ? { height: `${props.height}px`, width: `var(--dp-menu-min-width)` } : undefined,
     );
 
     const cellClassName = computed(() => ({