Bug 42231: (QA follow-up) Show item title in note and suspend-hold modals

The static 'hidden' attribute on #addNoteTitle and #suspendHoldTitle was never
removed, so the item title was populated but stayed invisible.

- Toggle 'hidden' off when a modal is populated with a title
- Toggle 'hidden' on when a modal is closed/cleared

Test plan:
- Enable AllowCheckoutNotes
- OPAC > Summary > Checked out: click 'Add note', confirm the item title shows
- OPAC > Summary > Holds: click 'Suspend', confirm the item title shows
- Reopen each modal on a different item, confirm the title updates
- Run an accessibility checker, confirm no empty-heading errors return

Signed-off-by: Paul Derscheid <paul.derscheid@lmscloud.de>
Signed-off-by: Pedro Amorim <pedro.amorim@openfifth.co.uk>

koha-tmpl/opac-tmpl/bootstrap/en/modules/opac-user.tt

@@ -1178,11 +1178,13 @@
                 var reserve_id = $(this).data("reserve_id");
                 $("#suspendHoldReserveId").val(reserve_id);
                 $("#suspendHoldTitle").html("<em>" + title + "</em>");
+                $("#suspendHoldTitle").prop("hidden", false);
                 $("#suspendHoldModal").modal("show");
             });
 
             $("#suspendHoldModal").on("hidden.bs.modal", function () {
                 $("#suspendHoldTitle").html("");
+                $("#suspendHoldTitle").prop("hidden", true);
                 $("#suspendHoldReserveId").val("");
                 suspend_until_date.clear();
             });
@@ -1358,6 +1360,7 @@
                 $("#addNote").val(note);
                 $("#addNoteIssueId").val(issue_id);
                 $("#addNoteTitle").text(title);
+                $("#addNoteTitle").prop("hidden", false);
                 $("#addNoteModal").modal("show");
             });
 
@@ -1371,6 +1374,7 @@
 
             $("#addNoteModal").on("hidden.bs.modal", function () {
                 $("#addNoteTitle").text("");
+                $("#addNoteTitle").prop("hidden", true);
                 $("#addNote").val("");
             });