fix: use hasSelection.value in assets empty-space click guard

hasSelection is a ComputedRef, so `if (hasSelection)` tested the wrapper
object and was always truthy, leaving the guard dead and running
clearSelection() on every empty-space click. Read `.value` so it only
clears when a selection actually exists.

src/components/sidebar/tabs/AssetsSidebarTab.vue

@@ -575,7 +575,7 @@ const handleDeselectAll = () => {
 }
 
 const handleEmptySpaceClick = () => {
-  if (hasSelection) {
+  if (hasSelection.value) {
     clearSelection()
   }
 }