fix: prevent cursor flickering when dragging slider handles

Fix issue where mouse cursor flickers between 'grabbing' and 'default'
while dragging slider handles. The cursor now remains 'grabbing'
throughout the entire drag operation regardless of mouse position.

Changes:
- Add dynamic 'is-dragging' class to SingleSlider and DualRangeSlider
- Apply cursor: grabbing to root component when dragging state is active

vue-widgets/src/components/shared/DualRangeSlider.vue

@@ -1,5 +1,5 @@
 <template>
-  <div class="dual-range-slider" :class="{ disabled, 'has-segments': scaleMode === 'segmented' && effectiveSegments.length > 0 }" @wheel="onWheel">
+  <div class="dual-range-slider" :class="{ disabled, 'is-dragging': dragging !== null, 'has-segments': scaleMode === 'segmented' && effectiveSegments.length > 0 }" @wheel="onWheel">
     <div class="slider-track" ref="trackEl">
       <!-- Background track -->
       <div class="slider-track__bg"></div>
@@ -331,6 +331,10 @@ onUnmounted(() => {
   pointer-events: none;
 }
 
+.dual-range-slider.is-dragging {
+  cursor: grabbing;
+}
+
 .slider-track {
   position: absolute;
   top: 14px;

vue-widgets/src/components/shared/SingleSlider.vue

@@ -1,5 +1,5 @@
 <template>
-  <div class="single-slider" :class="{ disabled }" @wheel="onWheel">
+  <div class="single-slider" :class="{ disabled, 'is-dragging': dragging }" @wheel="onWheel">
     <div class="slider-track" ref="trackEl">
       <div class="slider-track__bg"></div>
       <div
@@ -153,6 +153,10 @@ onUnmounted(() => {
   pointer-events: none;
 }
 
+.single-slider.is-dragging {
+  cursor: grabbing;
+}
+
 .slider-track {
   position: absolute;
   top: 14px;