fix(library): podcasts list newest episode first

A Jellypod podcast listed its episodes alphabetically. The store pinned
SortBy=SortName onto every drill-down, which overrode the order the
channel plugin returns — and since Jellypod prefixes played episodes with
"[Played]", the name sort also clumped every heard episode at the top.

Which order a container's children take is domain knowledge, so it moves
to Rust: the caller names the container (GetItemsOptions.parentKind) and
default_listing_sort answers with the sort. A channel folder is
PremiereDate descending, every other container keeps SortName ascending,
and a caller naming no container still gets no SortBy, so the paths that
rely on the server's own order keep it. An explicit sort always wins.

ChannelFolderItem with is_folder now maps to MediaKind::ChannelFolder
instead of collapsing into Folder — while both were Folder there was
nothing to key the rule on. The offline leg of the cache/server race
applies the same order, so the cached list no longer flashes in name
order before the server's arrives.

TRACES: UR-007 | DR-257 | UT-229, UT-230, UT-231

src/routes/library/+page.svelte

@@ -155,6 +155,7 @@
         case "album":
         case "artist":
         case "folder":
+        case "channelFolder":
         case "playlist":
         case "channel":
           // Navigate to detail view

src/routes/library/[id]/+page.svelte

@@ -171,7 +171,10 @@
         }
       }
 
-      await library.loadItems(itemId, { limit: 100 });
+      // Name the container so Rust can order its children: a podcast (a channel
+      // folder) is listed newest episode first, everything else by name.
+      // TRACES: UR-007 | DR-257
+      await library.loadItems(itemId, { limit: 100, parentKind: item?.kind });
 
       // Ensure cast/crew data is loaded for Movies, Series, and Episodes
       // Some APIs/caches may not include people data on first load
@@ -277,6 +280,7 @@
       case "album":
       case "artist":
       case "folder":
+      case "channelFolder":
       case "playlist":
       case "channel":
       case "movie":