refactor(device-sync): G.76 — extract browser + device-scan + job-events hooks + choose-folder util (cluster) (#643)

Four-cut cluster pulling the remaining lifecycle code out of
DeviceSync.tsx. 928 → 638 LOC (−290).

useDeviceSyncBrowser — playlists / randomAlbums / artists state +
their three loaders + the tab-switch useEffect that lazy-loads on
first visit + the 300 ms debounced album-search useEffect + the
expandedArtistIds / artistAlbumsMap / loadingArtistIds state with
toggleArtistExpand. Takes activeTab + search + a resetSearch
callback (so the tab-switch effect can clear the search input the
page still owns).

useDeviceSyncDeviceScan — scanDevice useCallback + the on-mount
useEffect + the auto-import-manifest useEffect (with the
manifestImportedRef gate so it only fires once per drive plug-in)
+ the clean-on-unplug useEffect that clears deviceFilePaths and
resets the import flag.

useDeviceSyncJobEvents — the device:sync:progress and
device:sync:complete event listeners. Complete handler dispatches
the toast, writes the manifest, generates per-playlist m3u8 files
(through fetchTracksForSource + trackToSyncInfo), and triggers
scanDevice. Cancelled state is preserved by re-calling
useDeviceSyncJobStore.cancel() after complete().

runDeviceSyncChooseFolder — the openDialog → setTargetDir →
optional manifest auto-import → scanDevice timer flow.

DeviceSync drops every direct import that those hooks now own
(getPlaylists, getArtists, getArtist, getAlbumList, searchSubsonic,
listen, openDialog, useEffect, useRef, SubsonicPlaylist /
SubsonicArtist / SubsonicAlbum type imports). Pure code move
otherwise — no behaviour change.

src/utils/runDeviceSyncChooseFolder.ts

@@ -0,0 +1,34 @@
+import { invoke } from '@tauri-apps/api/core';
+import { open as openDialog } from '@tauri-apps/plugin-dialog';
+import type { TFunction } from 'i18next';
+import { useDeviceSyncStore, type DeviceSyncSource } from '../store/deviceSyncStore';
+import { showToast } from './toast';
+
+export interface RunDeviceSyncChooseFolderDeps {
+  t: TFunction;
+  setTargetDir: (dir: string) => void;
+  scanDevice: () => Promise<void>;
+}
+
+export async function runDeviceSyncChooseFolder(deps: RunDeviceSyncChooseFolderDeps): Promise<void> {
+  const { t, setTargetDir, scanDevice } = deps;
+  const sel = await openDialog({ directory: true, multiple: false, title: t('deviceSync.chooseFolder') });
+  if (!sel) return;
+
+  const dir = sel as string;
+  setTargetDir(dir);
+  // If the device has a psysonic-sync.json, always import it — replacing any
+  // sources from a previous device so switching sticks works correctly.
+  try {
+    const manifest = await invoke<{ version: number; sources: DeviceSyncSource[] } | null>(
+      'read_device_manifest', { destDir: dir }
+    );
+    if (manifest?.sources?.length) {
+      useDeviceSyncStore.getState().clearSources();
+      manifest.sources.forEach(s => useDeviceSyncStore.getState().addSource(s));
+      showToast(t('deviceSync.manifestImported', { count: manifest.sources.length }), 4000, 'info');
+    }
+  } catch { /* no manifest, that's fine */ }
+  // Trigger a device scan after folder change
+  setTimeout(() => scanDevice(), 100);
+}