test(popover): cover open/close state and aria wiring

src/shared/ui/Popover/PopoverHarness.svelte

@@ -0,0 +1,21 @@
+<!--
+    Component: PopoverHarness
+    Test-only fixture: renders Popover with a button trigger and simple content
+    exposing the close() callback.
+-->
+<script lang="ts">
+import Popover from './Popover.svelte';
+
+let { open = $bindable(false) }: { open?: boolean } = $props();
+</script>
+
+<Popover bind:open>
+    {#snippet trigger(props)}
+        <button {...props}>Open</button>
+    {/snippet}
+    {#snippet children({ close })}
+        <div data-testid="content">
+            <button onclick={close} data-testid="close">Close</button>
+        </div>
+    {/snippet}
+</Popover>