refactor(api): F.51 — extract playlists + play queue + radio + statistics (#616)

Four more domain-eng modules out of `api/subsonic.ts`:

- `subsonicPlaylists.ts` — `getPlaylists`/`getPlaylist`/`createPlaylist`
  /`updatePlaylist`/`updatePlaylistMeta`/`uploadPlaylistCoverArt`/
  `uploadArtistImage`/`deletePlaylist`. The two upload helpers use
  the Tauri-side CORS bypass (`upload_playlist_cover` /
  `upload_artist_image`).
- `subsonicPlayQueue.ts` — `getPlayQueue`/`savePlayQueue`.
- `subsonicRadio.ts` — Internet Radio CRUD (4 fns), Tauri-side cover
  art ops (3 fns), RadioBrowser search/top + `fetchUrlBytes`.
- `subsonicStatistics.ts` — `fetchStatisticsLibraryAggregates`/
  `fetchStatisticsOverview`/`fetchStatisticsFormatSample` with their
  three per-server-folder caches and the `statisticsPageCacheKey`
  helper. `STATS_CACHE_TTL` renamed from the misleadingly-shared
  `RATING_CACHE_TTL` constant.

Also: drop ~20 now-unused type/value imports from `subsonic.ts`, trim
three orphan jsdoc comments left behind by earlier slices, fix four
`vi.mock` targets (`queueSync`, `playerStore.persistence`) plus the
dynamic `await import('../api/subsonic')` calls in `ContextMenu.tsx`
to point at the new module paths.

Pure code-move. subsonic.ts: 561 → 144 LOC (−417). What's left:
ping/pingWithCredentials/probeInstantMix/scheduleInstantMixProbe +
internal `apiWithCredentials`/`restBaseFromUrl`.

src/api/subsonicRadio.ts

@@ -0,0 +1,103 @@
+import { invoke } from '@tauri-apps/api/core';
+import { useAuthStore } from '../store/authStore';
+import { api } from './subsonicClient';
+import type { InternetRadioStation, RadioBrowserStation } from './subsonicTypes';
+
+export async function getInternetRadioStations(): Promise<InternetRadioStation[]> {
+  try {
+    const data = await api<{ internetRadioStations?: { internetRadioStation?: InternetRadioStation[] } }>(
+      'getInternetRadioStations.view'
+    );
+    return data.internetRadioStations?.internetRadioStation ?? [];
+  } catch {
+    return [];
+  }
+}
+
+export async function createInternetRadioStation(
+  name: string, streamUrl: string, homepageUrl?: string
+): Promise<void> {
+  const params: Record<string, unknown> = { name, streamUrl };
+  if (homepageUrl) params.homepageUrl = homepageUrl;
+  await api('createInternetRadioStation.view', params);
+}
+
+export async function updateInternetRadioStation(
+  id: string, name: string, streamUrl: string, homepageUrl?: string
+): Promise<void> {
+  const params: Record<string, unknown> = { id, name, streamUrl };
+  if (homepageUrl) params.homepageUrl = homepageUrl;
+  await api('updateInternetRadioStation.view', params);
+}
+
+export async function deleteInternetRadioStation(id: string): Promise<void> {
+  await api('deleteInternetRadioStation.view', { id });
+}
+
+export async function uploadRadioCoverArt(id: string, file: File): Promise<void> {
+  // Navidrome-specific endpoint — handled in Rust to bypass browser CORS restrictions.
+  const { getBaseUrl, getActiveServer } = useAuthStore.getState();
+  const server = getActiveServer();
+  const baseUrl = getBaseUrl();
+  const buffer = await file.arrayBuffer();
+  const fileBytes = Array.from(new Uint8Array(buffer));
+  await invoke('upload_radio_cover', {
+    serverUrl: baseUrl,
+    radioId: id,
+    username: server?.username ?? '',
+    password: server?.password ?? '',
+    fileBytes,
+    mimeType: file.type || 'image/jpeg',
+  });
+}
+
+export async function deleteRadioCoverArt(id: string): Promise<void> {
+  // Navidrome-specific endpoint — handled in Rust to bypass browser CORS restrictions.
+  const { getBaseUrl, getActiveServer } = useAuthStore.getState();
+  const server = getActiveServer();
+  const baseUrl = getBaseUrl();
+  await invoke('delete_radio_cover', {
+    serverUrl: baseUrl,
+    radioId: id,
+    username: server?.username ?? '',
+    password: server?.password ?? '',
+  });
+}
+
+export async function uploadRadioCoverArtBytes(id: string, fileBytes: number[], mimeType: string): Promise<void> {
+  const { getBaseUrl, getActiveServer } = useAuthStore.getState();
+  const server = getActiveServer();
+  const baseUrl = getBaseUrl();
+  await invoke('upload_radio_cover', {
+    serverUrl: baseUrl,
+    radioId: id,
+    username: server?.username ?? '',
+    password: server?.password ?? '',
+    fileBytes,
+    mimeType,
+  });
+}
+
+function parseRadioBrowserStations(raw: Array<Record<string, string>>): RadioBrowserStation[] {
+  return raw.map(s => ({
+    stationuuid: s.stationuuid ?? '',
+    name: s.name ?? '',
+    url: s.url ?? '',
+    favicon: s.favicon ?? '',
+    tags: s.tags ?? '',
+  }));
+}
+
+export async function searchRadioBrowser(query: string, offset = 0): Promise<RadioBrowserStation[]> {
+  const raw = await invoke<Array<Record<string, string>>>('search_radio_browser', { query, offset });
+  return parseRadioBrowserStations(raw);
+}
+
+export async function getTopRadioStations(offset = 0): Promise<RadioBrowserStation[]> {
+  const raw = await invoke<Array<Record<string, string>>>('get_top_radio_stations', { offset });
+  return parseRadioBrowserStations(raw);
+}
+
+export async function fetchUrlBytes(url: string): Promise<[number[], string]> {
+  return invoke<[number[], string]>('fetch_url_bytes', { url });
+}