feat(portal-rail-links): update icons for M3U playlist links

feat(portal-activity-item): add PortalAddedItem interface for recently-added catalog items

libs/shared/interfaces/src/lib/portal-activity-item.interface.ts

@@ -30,3 +30,8 @@ export interface PortalRecentItem extends PortalActivityItem {
 export interface PortalFavoriteItem extends PortalActivityItem {
     added_at: string;
 }
+
+/** A recently-added catalog item with an `added_at` timestamp. */
+export interface PortalAddedItem extends PortalActivityItem {
+    added_at: string;
+}