Make table sorting reachable by keyboard

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: MariusStorhaug

docs/overrides/assets/javascripts/tablesort.js

@@ -13,11 +13,16 @@ document$.subscribe(function () {
     }
     new Tablesort(table);
 
-    // Tablesort makes header cells focusable (tabindex=0) and sorts on click,
-    // but does not handle keyboard activation. Let Enter/Space sort too, so the
-    // sortable headers are usable without a mouse. Cover both th and td header
-    // cells, since a thead synthesized from the first row may hold td cells.
+    // Tablesort binds clicks to sortable headers. Make those cells focusable
+    // before adding Enter/Space activation. A synthesized thead may contain td.
     table.querySelectorAll("thead th, thead td").forEach(function (header) {
+      if (
+        header.getAttribute("role") !== "columnheader" ||
+        header.getAttribute("data-sort-method") === "none"
+      ) {
+        return;
+      }
+      header.tabIndex = 0;
       header.addEventListener("keydown", function (event) {
         if (event.key === "Enter" || event.key === " ") {
           event.preventDefault();