fix: reopen the merge dialog after dismissing it

frontend/src/routes/(root)/settings/libraries/[libraryId]/duplicates/+page.svelte

@@ -190,7 +190,16 @@
 		<MergeBooks
 			books={recordsFor(merging)}
 			libraryId={page.params.libraryId!}
-			open={true}
+			bind:open={
+				() => merging !== null,
+				(value) => {
+					// Bound, not passed as a bare `true`: the dialog closes itself on an
+					// outside click or Escape, and if that never reaches `merging` the
+					// group stays set — the button then re-assigns the same group,
+					// nothing changes, and the workbench never reopens.
+					if (!value) merging = null;
+				}
+			}
 			onmerged={() => (merging = null)}
 		/>
 	{/key}