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/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];
+        },
         [[], []],
     );
 }