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/runPlaylistZipDownload.ts

@@ -0,0 +1,36 @@
+import { invoke } from '@tauri-apps/api/core';
+import { join } from '@tauri-apps/api/path';
+import { buildDownloadUrl } from '../api/subsonicStreamUrl';
+import type { SubsonicPlaylist } from '../api/subsonicTypes';
+import { useZipDownloadStore } from '../store/zipDownloadStore';
+import { sanitizeFilename } from './playlistDetailHelpers';
+
+export interface RunPlaylistZipDownloadDeps {
+  playlist: SubsonicPlaylist;
+  id: string;
+  downloadFolder: string | null;
+  requestDownloadFolder: () => Promise<string | null>;
+  setZipDownloadId: (id: string | null) => void;
+}
+
+export async function runPlaylistZipDownload(deps: RunPlaylistZipDownloadDeps): Promise<void> {
+  const { playlist, id, downloadFolder, requestDownloadFolder, setZipDownloadId } = deps;
+  const folder = downloadFolder || await requestDownloadFolder();
+  if (!folder) return;
+
+  const filename = `${sanitizeFilename(playlist.name)}.zip`;
+  const destPath = await join(folder, filename);
+  const url = buildDownloadUrl(id);
+  const downloadId = crypto.randomUUID();
+
+  const { start, complete, fail } = useZipDownloadStore.getState();
+  start(downloadId, filename);
+  setZipDownloadId(downloadId);
+  try {
+    await invoke('download_zip', { id: downloadId, url, destPath });
+    complete(downloadId);
+  } catch (e) {
+    fail(downloadId);
+    console.error('ZIP download failed:', e);
+  }
+}