feat(feed): Show chips in the toolbar + key+direction sort

1) Move the Show view filter (Unwatched/In progress/All/Watched/Hidden) up into the
   toolbar chip row as its own single-select group, divided from the content-type chips;
   removed the 'show' sidebar widget (sidebar now = Upload date / Language / Topic).
2) Rework ordering like the Playlists page: a sort-key dropdown (Date, Popular, Duration,
   Name, Channel subscribers, Channel priority, Surprise me) + a single asc/desc arrow
   toggle, instead of separate directional entries. 'Most viewed' is now 'Popular'.
   Backend gains the missing directions (views_asc, title_desc, subscribers_asc,
   priority_asc); the frontend maps (key, dir) -> the backend sort string, so FeedFilters
   is unchanged. Trilingual (feed.sortKey.*, feed.dirAsc/dirDesc). Feed.tsx normalized to LF.

frontend/src/components/Sidebar.tsx

@@ -214,7 +214,6 @@ export default function Sidebar({
   }
 
   const available: Record<WidgetId, boolean> = {
-    show: true,
     date: true,
     language: languages.length > 0,
     topic: topics.length > 0,
@@ -237,24 +236,6 @@ export default function Sidebar({
 
   function widgetBody(id: WidgetId): React.ReactNode {
     switch (id) {
-      case "show":
-        return (
-          <div className="grid grid-cols-2 gap-1.5">
-            {SHOW_IDS.map((id) => (
-              <button
-                key={id}
-                onClick={() => setFilters({ ...filters, show: id })}
-                className={`text-xs py-1.5 rounded-lg border shadow-sm active:translate-y-px transition ${
-                  filters.show === id
-                    ? "bg-accent text-accent-fg border-accent"
-                    : "bg-card border-border hover:border-accent"
-                }`}
-              >
-                {t("sidebar.show." + id)}
-              </button>
-            ))}
-          </div>
-        );
       case "date":
         return (
           <>