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>