refactor: clear remaining lint errors (comma operator, bind:this ref)

- splitArray: replace the comma-operator reduce body with an explicit
  block + return (no-sequences); behaviour unchanged
- BreadcrumbHeaderSeeded: declare the bind:this ref with $state() so it
  is not flagged as never-assigned (oxlint cannot see template bindings),
  matching the rest of the codebase; guard the onMount use

src/features/Breadcrumb/ui/BreadcrumbHeader/BreadcrumbHeaderSeeded.svelte

@@ -11,10 +11,14 @@ const sections = [
     { index: 102, title: 'Spacing' },
 ];
 
-/** @type {HTMLDivElement} */
-let container;
+/** @type {HTMLDivElement | undefined} */
+let container = $state();
 
 onMount(() => {
+    if (!container) {
+        return;
+    }
+
     for (const section of sections) {
         const el = /** @type {HTMLElement} */ (container.querySelector(`[data-story-index="${section.index}"]`));
         scrollBreadcrumbsStore.add({ index: section.index, title: section.title, element: el }, 96);

src/shared/lib/utils/splitArray/splitArray.ts

@@ -24,9 +24,14 @@
  */
 export function splitArray<T>(array: T[], callback: (item: T) => boolean) {
     return array.reduce<[T[], T[]]>(
-        ([pass, fail], item) => (
-            callback(item) ? pass.push(item) : fail.push(item), [pass, fail]
-        ),
+        ([pass, fail], item) => {
+            if (callback(item)) {
+                pass.push(item);
+            } else {
+                fail.push(item);
+            }
+            return [pass, fail];
+        },
         [[], []],
     );
 }