refactor(core): consolidate shared app foundations

lib/mixins/paginated_item_loader.dart

@@ -96,6 +96,43 @@ mixin PaginatedItemLoader<T, W extends StatefulWidget> on State<W> {
     return (page: result, applied: true);
   }
 
+  /// Shared initial-load transaction for paginated consumers.
+  ///
+  /// Owns reset, stale-result rejection, mounted checks, and error-state
+  /// application. Callers supply only their view fields, logging, and
+  /// post-success behavior.
+  Future<bool> loadInitialPaginatedItems({
+    required int pageSize,
+    required VoidCallback resetViewState,
+    required void Function(List<T> items) applyLoadedItems,
+    required void Function(Object error, StackTrace stackTrace) applyError,
+    void Function(int loadedCount, int totalCount)? onLoaded,
+    void Function(Object error, StackTrace stackTrace)? onError,
+  }) async {
+    setState(() {
+      resetViewState();
+      resetPaginationState();
+    });
+
+    try {
+      final initialPage = await loadInitialPageWithStatus(pageSize);
+      if (!initialPage.applied || !mounted) return false;
+
+      setState(() {
+        applyLoadedItems(loadedItems.values.toList());
+      });
+      onLoaded?.call(loadedItems.length, totalSize);
+      return true;
+    } catch (error, stackTrace) {
+      onError?.call(error, stackTrace);
+      if (!mounted) return false;
+      setState(() {
+        applyError(error, stackTrace);
+      });
+      return false;
+    }
+  }
+
   /// Fetch any unloaded items inside [firstIndex, firstIndex + visibleCount)
   /// with [buffer] extra indices on each side. Serialized — only one
   /// range-fetch runs at a time — and re-checks after each success so a