don't remount the virtualizer on every selection change

ComboboxVirtualizer was keyed on JSON.stringify(modelValue), which
forced a full destroy + remount of the virtualizer (and every rendered
row) on every selection toggle. In a long multi-select dropdown this
threw away the user's scroll position on each click and re-ran all the
row mounting work, plus the JSON.stringify itself.

The key isn't needed: row selected styling comes from
:class="itemClasses({ selected: isSelected(option) })", which is
already reactive on modelValue, so individual rows re-style themselves
without needing the virtualizer to remount. Verified that both
selecting and deselecting a row in a multi-select with 20 options
updates the blue selected styling and preserves scroll position.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: jasonvarga

resources/js/components/ui/Combobox/Combobox.vue

@@ -476,7 +476,6 @@ defineExpose({
 
                                 <ComboboxVirtualizer
                                     v-if="filteredOptions.length"
-                                    :key="JSON.stringify(modelValue)"
                                     :estimate-size="40"
                                     :options="filteredOptions"
                                     :text-content="(opt) => getOptionLabel(opt)"