refactor(playlist): G.66 — extract ZIP download + bulk play + row drag + reorder drop (cluster) (#633)

Four-cut cluster pulling action bodies out of PlaylistDetail.tsx. 741
→ 635 LOC (−106). Each handler on the page becomes a thin wrapper
around a parameterized utility; pure code move, no behaviour change.

runPlaylistZipDownload — the buildDownloadUrl → invoke('download_zip')
flow with start/complete/fail dispatches to useZipDownloadStore and
the setZipDownloadId hand-off. Takes playlist + id + downloadFolder
+ requestDownloadFolder + the id-setter as deps. PlaylistDetail
loses the invoke / join / buildDownloadUrl / sanitizeFilename imports
that only this handler used.

playlistBulkPlayActions — three exports (playPlaylistAll,
shufflePlaylistAll, enqueuePlaylistAll) with a shared BulkPlayDeps
shape (songsLength + id + tracks + touchPlaylist + playTrack +
enqueue). Same length-guard, same touchPlaylist call, same
shuffle / play / enqueue branches as before.

startPlaylistRowDrag — the threshold-drag dispatch on row mousedown
(5px deadzone, then bulk-songs / playlist-reorder / single-song
payload depending on selection state + filtered-view flag). Takes
the mouse event + idx + songs + selectedIds + isFiltered + startDrag.

runPlaylistReorderDrop — the psy-drop event handler that lives
inside the tracklist useEffect. Parses the custom-event detail,
computes from→to indexes, and updates songs + savePlaylist + clears
dropTargetIdx. The useEffect itself stays in the page because it
wires up the event listener.

PlaylistDetail's import list also drops `invoke`, `join`,
`buildDownloadUrl`, `sanitizeFilename` — they followed the ZIP
helper to its new file.

src/utils/playlistBulkPlayActions.ts

@@ -0,0 +1,36 @@
+import type { Track } from '../store/playerStoreTypes';
+
+export interface BulkPlayDeps {
+  songsLength: number;
+  id: string | undefined;
+  tracks: Track[];
+  touchPlaylist: (id: string) => void;
+  playTrack: (track: Track, queue: Track[]) => void;
+  enqueue: (tracks: Track[]) => void;
+}
+
+export function playPlaylistAll(deps: BulkPlayDeps): void {
+  const { songsLength, id, tracks, touchPlaylist, playTrack } = deps;
+  if (!songsLength || !id) return;
+  touchPlaylist(id);
+  playTrack(tracks[0], tracks);
+}
+
+export function shufflePlaylistAll(deps: BulkPlayDeps): void {
+  const { songsLength, id, tracks, touchPlaylist, playTrack } = deps;
+  if (!songsLength || !id) return;
+  touchPlaylist(id);
+  const shuffled = [...tracks];
+  for (let i = shuffled.length - 1; i > 0; i--) {
+    const j = Math.floor(Math.random() * (i + 1));
+    [shuffled[i], shuffled[j]] = [shuffled[j], shuffled[i]];
+  }
+  playTrack(shuffled[0], shuffled);
+}
+
+export function enqueuePlaylistAll(deps: BulkPlayDeps): void {
+  const { songsLength, id, tracks, touchPlaylist, enqueue } = deps;
+  if (!songsLength || !id) return;
+  touchPlaylist(id);
+  enqueue(tracks);
+}