feat(plex): 'last watched' browse sort + auto-apply in the in-progress view (S3)

Add a 'lastwatched' sort key to the unified Plex browse. Movies rank by
coalesce(progress_updated_at, watched_at); shows by max(coalesce(...)) across
their episodes (rollup.resumed_at, now broadened from progress-only so watched
episodes count too). Never-watched titles sink via nullslast.

Frontend auto-applies lastwatched:desc when entering the in-progress watch-state
view and restores the pre-entry sort on exit; a manual sort change while there
still wins. i18n HU+EN. Backend tests cover both union legs + mixed nullslast.

frontend/src/components/PlexBrowse.tsx

@@ -11,6 +11,7 @@ import { User, X } from "lucide-react";
 import { qk } from "../lib/queryKeys";
 import { healPlexField } from "../lib/plexSearch";
 import { healPlexSort, plexSortOptions, PLEX_SORT_FALLBACK } from "../lib/plexSort";
+import type { SortState } from "../lib/columnSort";
 import {
   api,
   EMPTY_PLEX_FILTERS,
@@ -52,6 +53,13 @@ const PlexCollectionView = lazy(() => import("./PlexCollectionView"));
 
 const PAGE = 40;
 
+// D3: the "last watched" sort auto-applied when you enter the in-progress watch-state view (most
+// recently watched first). Frozen for the same reason as PLEX_SORT_FALLBACK (handed out by reference).
+const LASTWATCHED_SORT: NonNullable<SortState> = Object.freeze({
+  key: "lastwatched",
+  dir: "desc" as const,
+});
+
 // Watch-state options for the toolbar pill (moved out of the filter rail — it's a top-level "what am
 // I looking at" control now, like the feed's Watch-state pill, not a rail widget).
 const SHOW_OPTS = ["all", "unwatched", "in_progress", "watched"] as const;
@@ -185,6 +193,25 @@ export default function PlexBrowse() {
     return () => window.removeEventListener("keydown", onKey);
   }, [sub]);
 
+  // D3: entering the in-progress watch-state view auto-applies the "last watched" sort (most recently
+  // watched first); leaving restores the sort that was active before entering. Only the ENTER edge
+  // forces the sort, so a manual sort change while in the in-progress view still wins — it's just not
+  // carried back out (exit returns to the pre-entry preference). We stash the raw provider `sort`, not
+  // the scope-healed one, so the user's real preference round-trips.
+  const prevShow = useRef(show);
+  const preInProgressSort = useRef<SortState | null>(null);
+  useEffect(() => {
+    const was = prevShow.current;
+    if (was !== "in_progress" && show === "in_progress") {
+      preInProgressSort.current = sort;
+      setSort(LASTWATCHED_SORT);
+    } else if (was === "in_progress" && show !== "in_progress") {
+      if (preInProgressSort.current) setSort(preInProgressSort.current);
+      preInProgressSort.current = null;
+    }
+    prevShow.current = show;
+  }, [show, sort, setSort]);
+
   const browseQ = useInfiniteQuery({
     queryKey: qk.plexLibrary(scope, dq, sortState, show, filters, fieldState, lang),
     // Gate on committedLang so a language switch fires ONE fetch (after the genre-clear effect

frontend/src/i18n/locales/en/plex.json

@@ -45,6 +45,7 @@
   },
   "sort": {
     "added": "Recently added",
+    "lastwatched": "Last watched",
     "title": "Title",
     "year": "Year",
     "rating": "IMDb rating",

frontend/src/i18n/locales/hu/plex.json

@@ -45,6 +45,7 @@
   },
   "sort": {
     "added": "Nemrég hozzáadott",
+    "lastwatched": "Utoljára nézve",
     "title": "Cím",
     "year": "Év",
     "rating": "IMDb pont",

frontend/src/lib/plexSort.ts

@@ -4,8 +4,16 @@ import { healSort, type SortOption, type SortState } from "./columnSort";
 // SortControl. Direction lives in the SortState (no more sibling `sortDir` on PlexFilters); the wire
 // call (`plexLibrary`) still splits it into `sort` + `sort_dir` at the server boundary.
 
-const MOVIE_SORTS = ["added", "release", "year", "rating", "duration", "title"] as const;
-const SHOW_SORTS = ["added", "release", "year", "rating", "title"] as const;
+const MOVIE_SORTS = [
+  "added",
+  "lastwatched",
+  "release",
+  "year",
+  "rating",
+  "duration",
+  "title",
+] as const;
+const SHOW_SORTS = ["added", "lastwatched", "release", "year", "rating", "title"] as const;
 
 /** The sort keys a scope offers — movie libraries add `duration`; shows/both don't. */
 function plexSortKeys(scope: string): string[] {