refactor(api): F.48 — extract subsonic types + client primitives (#613)

First Phase F slice. Splits the 1333-LOC `api/subsonic.ts` along its
two most obvious axes:

- `subsonicTypes.ts` — all ~24 exported interfaces + type aliases
  (album/song/artist/playlist/directory/genre/now-playing/radio,
  random-songs filters, three statistics shapes, search + starred
  results, AlbumInfo, structured-lyrics types, etc.) plus the
  `RADIO_PAGE_SIZE` constant.
- `subsonicClient.ts` — token-auth + `getClient` + `api<T>()` +
  `libraryFilterParams` + `secureRandomSalt` / `getAuthParams` /
  `SUBSONIC_CLIENT`. The credential-bearing API helpers
  (`pingWithCredentials`, `apiWithCredentials`, `restBaseFromUrl`,
  `probeInstantMixWithCredentials`) stay in `subsonic.ts` for now —
  they could move into the client module in a follow-up.

66 external call sites migrated to direct imports from the new
modules (no re-export shims in `subsonic.ts`). Pure code-move;
contract test stays green.

subsonic.ts: 1333 → 1078 LOC (−255).

src/utils/applySharePaste.ts

@@ -1,7 +1,8 @@
+import type { SubsonicSong } from '../api/subsonicTypes';
 import { songToTrack } from '../utils/songToTrack';
 import type { NavigateFunction } from 'react-router-dom';
 import type { TFunction } from 'i18next';
-import { getAlbum, getArtist, getSong, type SubsonicSong } from '../api/subsonic';
+import { getAlbum, getArtist, getSong } from '../api/subsonic';
 import { useAuthStore } from '../store/authStore';
 import { usePlayerStore } from '../store/playerStore';
 import { findServerIdForShareUrl, type EntitySharePayloadV1 } from './shareLink';

src/utils/exportAlbumCard.ts

@@ -1,6 +1,7 @@
+import type { SubsonicAlbum } from '../api/subsonicTypes';
 import React from 'react';
 import { renderToStaticMarkup } from 'react-dom/server';
-import { buildCoverArtUrl, coverArtCacheKey, SubsonicAlbum } from '../api/subsonic';
+import { buildCoverArtUrl, coverArtCacheKey } from '../api/subsonic';
 import { getCachedBlob } from './imageCache';
 import PsysonicLogo from '../components/PsysonicLogo';
 

src/utils/exportNewAlbums.ts

@@ -1,9 +1,8 @@
+import type { SubsonicAlbum } from '../api/subsonicTypes';
 import { writeFile } from '@tauri-apps/plugin-fs';
 import { downloadDir, join } from '@tauri-apps/api/path';
 import { getAlbumList, buildCoverArtUrl } from '../api/subsonic';
 import { useAuthStore } from '../store/authStore';
-import type { SubsonicAlbum } from '../api/subsonic';
-
 // Catppuccin Macchiato palette
 const M = {
   crust:    '#181926',

src/utils/luckyMix.ts

@@ -1,15 +1,7 @@
+import type { SubsonicAlbum, SubsonicSong } from '../api/subsonicTypes';
 import type { Track } from '../store/playerStoreTypes';
 import { songToTrack } from '../utils/songToTrack';
-import {
-  filterSongsToActiveLibrary,
-  getAlbum,
-  getAlbumList,
-  getRandomSongs,
-  getSimilarSongs,
-  getTopSongs,
-  type SubsonicAlbum,
-  type SubsonicSong,
-} from '../api/subsonic';
+import { filterSongsToActiveLibrary, getAlbum, getAlbumList, getRandomSongs, getSimilarSongs, getTopSongs } from '../api/subsonic';
 import { invoke } from '@tauri-apps/api/core';
 import i18n from '../i18n';
 import { useAuthStore } from '../store/authStore';

src/utils/mixRatingFilter.ts

@@ -1,11 +1,5 @@
-import {
-  getRandomSongs,
-  parseSubsonicEntityStarRating,
-  prefetchAlbumUserRatings,
-  prefetchArtistUserRatings,
-  type SubsonicAlbum,
-  type SubsonicSong,
-} from '../api/subsonic';
+import type { SubsonicAlbum, SubsonicSong } from '../api/subsonicTypes';
+import { getRandomSongs, parseSubsonicEntityStarRating, prefetchAlbumUserRatings, prefetchArtistUserRatings } from '../api/subsonic';
 import { useAuthStore } from '../store/authStore';
 
 /** Default target list size for Random Mix; per-call override via `fetchRandomMixSongsUntilFull(c, { targetSize })`. */

src/utils/playSong.ts

@@ -1,7 +1,6 @@
+import type { SubsonicSong } from '../api/subsonicTypes';
 import { songToTrack } from '../utils/songToTrack';
 import { usePlayerStore } from '../store/playerStore';
-import type { SubsonicSong } from '../api/subsonic';
-
 function fadeOut(setVolume: (v: number) => void, from: number, durationMs: number): Promise<void> {
   return new Promise(resolve => {
     const steps = 16;

src/utils/songToTrack.ts

@@ -1,5 +1,5 @@
+import type { SubsonicSong } from '../api/subsonicTypes';
 import type { Track } from '../store/playerStoreTypes';
-import type { SubsonicSong } from '../api/subsonic';
 export function songToTrack(song: SubsonicSong): Track {
   return {
     id: song.id,