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/i18n/locales/de/feed.json

@@ -9,6 +9,17 @@
   "videoCount_one": "{{formattedCount}} Video",
   "videoCount_other": "{{formattedCount}} Videos",
   "sortLabel": "Sortierung",
+  "dirAsc": "Aufsteigend",
+  "dirDesc": "Absteigend",
+  "sortKey": {
+    "date": "Datum",
+    "popular": "Beliebt",
+    "duration": "Dauer",
+    "title": "Name",
+    "subscribers": "Kanal-Abonnenten",
+    "priority": "Kanal-Priorität",
+    "shuffle": "Überraschung"
+  },
   "loadingMore": "Mehr wird geladen…",
   "hiddenNamed": "Ausgeblendet: „{{title}}”",
   "hidden": "Video ausgeblendet",