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-tauri/src/domain/search_rank.rs

@@ -53,7 +53,11 @@ fn kind_rank(kind: MediaKind) -> u8 {
         // Top-level containers a user is most likely to be looking for.
         MediaKind::Series | MediaKind::Movie | MediaKind::Album | MediaKind::Artist => 0,
         // Sub-containers and standalone collections.
-        MediaKind::Season | MediaKind::Playlist | MediaKind::Channel | MediaKind::Folder => 1,
+        MediaKind::Season
+        | MediaKind::Playlist
+        | MediaKind::Channel
+        | MediaKind::ChannelFolder
+        | MediaKind::Folder => 1,
         // Leaves — an episode/track is a match *inside* something bigger.
         MediaKind::Episode | MediaKind::Track | MediaKind::LiveChannel | MediaKind::ChannelItem => {
             2