refactor(api): F.50 — extract 7 small domain modules (#615)

Seven domain-eng splits peel ~200 LOC of read endpoints out of
`api/subsonic.ts`:

- `subsonicStreamUrl.ts` — `buildStreamUrl`, `coverArtCacheKey`,
  `buildCoverArtUrl`, `buildDownloadUrl` (token-signed URL builders
  for the four /rest endpoints we hand to the browser).
- `subsonicStarRating.ts` — `getStarred`, `star`, `unstar`,
  `setRating`, `probeEntityRatingSupport`. `setRating` still triggers
  the lazy `navidromeBrowse` cache invalidation; the same-folder
  lazy import path is preserved.
- `subsonicSearch.ts` — `search`, `searchSongsPaged`.
- `subsonicScrobble.ts` — `scrobbleSong`, `reportNowPlaying`,
  `getNowPlaying`.
- `subsonicAlbumInfo.ts` — `getAlbumInfo2`.
- `subsonicLyrics.ts` — `getLyricsBySongId`.
- `subsonicGenres.ts` — `getGenres`, `getAlbumsByGenre`.

63 external call sites migrated to direct imports. Four `vi.mock`
targets in the store-level tests pointed at `../api/subsonic` and
were updated to the new module paths.

Pure code-move. subsonic.ts: 762 → 561 LOC (−201).

src/utils/exportAlbumCard.ts

@@ -1,7 +1,7 @@
+import { buildCoverArtUrl, coverArtCacheKey } from '../api/subsonicStreamUrl';
 import type { SubsonicAlbum } from '../api/subsonicTypes';
 import React from 'react';
 import { renderToStaticMarkup } from 'react-dom/server';
-import { buildCoverArtUrl, coverArtCacheKey } from '../api/subsonic';
 import { getCachedBlob } from './imageCache';
 import PsysonicLogo from '../components/PsysonicLogo';
 

src/utils/exportNewAlbums.ts

@@ -1,8 +1,8 @@
+import { buildCoverArtUrl } from '../api/subsonicStreamUrl';
 import { getAlbumList } from '../api/subsonicLibrary';
 import type { SubsonicAlbum } from '../api/subsonicTypes';
 import { writeFile } from '@tauri-apps/plugin-fs';
 import { downloadDir, join } from '@tauri-apps/api/path';
-import { buildCoverArtUrl } from '../api/subsonic';
 import { useAuthStore } from '../store/authStore';
 // Catppuccin Macchiato palette
 const M = {

src/utils/resolvePlaybackUrl.ts

@@ -1,4 +1,4 @@
-import { buildStreamUrl } from '../api/subsonic';
+import { buildStreamUrl } from '../api/subsonicStreamUrl';
 import { useOfflineStore } from '../store/offlineStore';
 import { useHotCacheStore } from '../store/hotCacheStore';