refactor(playlist): G.69 — extract runPlaylistLoad + usePlaylistPreview + usePlaylistBulkPlayCallbacks + usePlaylistDerived (cluster) (#636)

Four-cut cluster pulling the remaining handler bodies + memo island
out of PlaylistDetail.tsx. 507 → 437 LOC (−70).

runPlaylistLoad — async fetch + populate flow that the load
useEffect drives: getPlaylist → filterSongsToActiveLibrary →
setPlaylist + setSongs + setCustomCoverId from playlist.coverArt +
rebuild ratings + starredSongs from each song's stored userRating /
starred flag. Takes the six setters as deps. Page keeps the
useEffect that calls it on id / lastModified change.

usePlaylistPreview — startPreview callback (dispatches into
previewStore with the 'suggestions' source) plus the unmount-time
stopPreview cleanup. Returns just { startPreview }. No props
needed.

usePlaylistBulkPlayCallbacks — wraps playPlaylistAll /
shufflePlaylistAll / enqueuePlaylistAll utilities behind three
useCallback handles with the right deps array. Takes
{ songsLength, id, tracks, touchPlaylist, playTrack, enqueue }.

usePlaylistDerived — existingIds, tracks (songToTrack), sorted +
filtered displayedSongs via getDisplayedSongs, displayedTracks (with
the cheap aliasing optimization when displayedSongs === songs),
isFiltered. Subscribes to playerStore's userRatingOverrides +
starredOverrides directly so the page no longer threads them through
the memo deps.

PlaylistDetail drops these direct imports — they followed the new
modules: getPlaylist, filterSongsToActiveLibrary, songToTrack,
useMemo, getDisplayedSongs (now type-only),
playPlaylistAll/shuffle/enqueue from playlistBulkPlayActions.
Pure code move otherwise.

src/hooks/usePlaylistBulkPlayCallbacks.ts

@@ -0,0 +1,39 @@
+import { useCallback } from 'react';
+import type { Track } from '../store/playerStoreTypes';
+import { enqueuePlaylistAll, playPlaylistAll, shufflePlaylistAll } from '../utils/playlistBulkPlayActions';
+
+export interface PlaylistBulkPlayCallbacksDeps {
+  songsLength: number;
+  id: string | undefined;
+  tracks: Track[];
+  touchPlaylist: (id: string) => void;
+  playTrack: (track: Track, queue: Track[]) => void;
+  enqueue: (tracks: Track[]) => void;
+}
+
+export interface PlaylistBulkPlayCallbacks {
+  handlePlayAll: () => void;
+  handleShuffleAll: () => void;
+  handleEnqueueAll: () => void;
+}
+
+export function usePlaylistBulkPlayCallbacks(deps: PlaylistBulkPlayCallbacksDeps): PlaylistBulkPlayCallbacks {
+  const { songsLength, id, tracks, touchPlaylist, playTrack, enqueue } = deps;
+
+  const handlePlayAll = useCallback(
+    () => playPlaylistAll({ songsLength, id, tracks, touchPlaylist, playTrack, enqueue }),
+    [songsLength, id, tracks, touchPlaylist, playTrack, enqueue],
+  );
+
+  const handleShuffleAll = useCallback(
+    () => shufflePlaylistAll({ songsLength, id, tracks, touchPlaylist, playTrack, enqueue }),
+    [songsLength, id, tracks, touchPlaylist, playTrack, enqueue],
+  );
+
+  const handleEnqueueAll = useCallback(
+    () => enqueuePlaylistAll({ songsLength, id, tracks, touchPlaylist, playTrack, enqueue }),
+    [songsLength, id, tracks, touchPlaylist, playTrack, enqueue],
+  );
+
+  return { handlePlayAll, handleShuffleAll, handleEnqueueAll };
+}