fix: Prevent multiple asset card popovers from opening simultaneously (#6808)

## Summary

Ensures only one MediaAssetCard popover is open at a time.

## Changes

- Added `hide()` method exposure in MoreButton component
- Implemented parent-level state management for tracking open popover
- Added VueUse `whenever` to auto-close other popovers when one opens

## Test Plan

- Open multiple asset cards' more menus
- Verify only one popover remains open at a time

🤖 Generated with [Claude Code](https://claude.com/claude-code)

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6808-fix-Prevent-multiple-asset-card-popovers-from-opening-simultaneously-2b26d73d365081e1b3f0d97b869cedc5)
by [Unito](https://www.unito.io)

src/components/button/MoreButton.vue

@@ -68,4 +68,8 @@ const toggle = (event: Event) => {
 const hide = () => {
   popover.value?.hide()
 }
+
+defineExpose({
+  hide
+})
 </script>

src/components/sidebar/tabs/AssetsSidebarTab.vue

@@ -85,10 +85,13 @@
               :show-output-count="shouldShowOutputCount(item)"
               :output-count="getOutputCount(item)"
               :show-delete-button="shouldShowDeleteButton"
+              :open-popover-id="openPopoverId"
               @click="handleAssetSelect(item)"
               @zoom="handleZoomClick(item)"
               @output-count-click="enterFolderView(item)"
               @asset-deleted="refreshAssets"
+              @popover-opened="openPopoverId = item.id"
+              @popover-closed="openPopoverId = null"
             />
           </template>
         </VirtualGrid>
@@ -199,6 +202,9 @@ const folderPromptId = ref<string | null>(null)
 const folderExecutionTime = ref<number | undefined>(undefined)
 const isInFolderView = computed(() => folderPromptId.value !== null)
 
+// Track which asset's popover is open (for single-instance popover management)
+const openPopoverId = ref<string | null>(null)
+
 // Determine if delete button should be shown
 // Hide delete button when in input tab and not in cloud (OSS mode - files are from local folders)
 const shouldShowDeleteButton = computed(() => {