htmlreport: preserve filter state when navigating back/forward

Currently, using browser back/forward buttons resets filtered issue lists,
even though checkbox states persist. This is confusing and makes it hard to
see the filtered results consistently.

Changes:
- Added a `reapplyFilters()` function that reapplies ID, severity,
  classification, and tool filters based on the current checkbox states.
- Hooked `reapplyFilters()` to the `pageshow` event to restore filtered
  classes when navigating with back/forward.

Author: rgetz

htmlreport/cppcheck-htmlreport

@@ -356,6 +356,57 @@ HTML_HEAD = """
         }
       }
 
+      function reapplyFilters() {
+        // Reapply ID filters
+        var idToggles = document.querySelectorAll(".idToggle");
+        for (var i = 1; i < idToggles.length; i++) {
+          var cb = idToggles[i];
+          var elements = document.querySelectorAll("." + cb.id);
+          for (var j = 0; j < elements.length; j++) {
+            elements[j].classList.toggle("id-filtered", !cb.checked);
+          }
+        }
+
+        // Reapply severity filters
+        var sevToggles = document.querySelectorAll(".sev_toggle");
+        for (var i = 0; i < sevToggles.length; i++) {
+          var cb = sevToggles[i];
+            var elements = document.querySelectorAll(".sev_" + cb.id);
+          for (var j = 0; j < elements.length; j++) {
+            elements[j].classList.toggle("severity-filtered", !cb.checked);
+          }
+        }
+
+        // Reapply classification filters
+        var classToggles = document.querySelectorAll(".class_toggle");
+        for (var i = 0; i < classToggles.length; i++) {
+          var cb = classToggles[i];
+          var elements = document.querySelectorAll(".class_" + cb.id);
+          for (var j = 0; j < elements.length; j++) {
+            elements[j].classList.toggle("classification-filtered", !cb.checked);
+          }
+        }
+
+        // Reapply tool filters
+        var toolToggles = document.querySelectorAll(".tool_toggle");
+        for (var i = 0; i < toolToggles.length; i++) {
+          var cb = toolToggles[i];
+          var elements;
+          if (cb.id == "clang-tidy")
+            elements = document.querySelectorAll("[class^=clang-tidy-]");
+          else
+            elements = document.querySelectorAll(".issue:not([class^=clang-tidy-])");
+
+          for (var j = 0; j < elements.length; j++) {
+            elements[j].classList.toggle("tool-filtered", !cb.checked);
+          }
+        }
+
+        // Update file rows
+        updateFileRows();
+      }
+
+      window.addEventListener("pageshow", reapplyFilters);
       window.addEventListener("load", initExpandables);
     </script>
   </head>