refactor(fullscreen-player): H5 — split FullscreenPlayer.tsx 911 → 228 LOC across 11 files (#668)

* refactor(fullscreen-player): H5 — extract FsLyricsApple + FsLyricsRail + useWordLyricsSync

The two lyrics views become own files under components/fullscreenPlayer/.
Their identical word-sync imperative DOM-update useEffect (only differing in
the .fsa-/.fsr- class prefix) collapses into the shared useWordLyricsSync
hook with a classPrefix arg.

FullscreenPlayer.tsx: 911 → 613 LOC.

* refactor(fullscreen-player): H5 — extract FsArt + FsPortrait + FsSeekbar

The three visual subcomponents move into own files. formatTime moves into
utils/fullscreenPlayerHelpers.ts so FsSeekbar keeps using it.

FullscreenPlayer.tsx: 613 → 421 LOC.

* refactor(fullscreen-player): H5 — extract FsLyricsMenu + FsPlayBtn

The lyrics-settings popover and the isolated play/pause button move into
own files. FullscreenPlayer drops the now-unused lucide-react icons
(Play/Pause/Moon/Sunrise/Music) and the PlaybackDelayModal +
PlaybackScheduleBadge imports — both used only by FsPlayBtn now.

FullscreenPlayer.tsx: 421 → 304 LOC.

* refactor(fullscreen-player): H5 — extract useFsDynamicAccent + useFsArtistPortrait + useFsIdleFade

Pulls three state+effect islands out of FullscreenPlayer:
  - useFsDynamicAccent owns the cover-blob fetch + extractCoverColors call
    plus the module-level artKey → accent cache that makes same-album song
    switches instant.
  - useFsArtistPortrait fetches getArtistInfo().largeImageUrl for the right-
    side portrait, returning '' until resolved (or when no artistId).
  - useFsIdleFade flips isIdle true after 3 s of inactivity, exposes a
    throttled mousemove handler, and binds Escape to the provided callback.

FullscreenPlayer.tsx: 304 → 228 LOC.

src/hooks/useFsArtistPortrait.ts

@@ -0,0 +1,19 @@
+import { useEffect, useState } from 'react';
+import { getArtistInfo } from '../api/subsonicArtists';
+
+/** Fetches the large artist image for the given artist id, returning '' until
+ *  the request resolves (or when there is no artist id). Falls through silently
+ *  on network failures — the caller should layer a cover-art fallback on top. */
+export function useFsArtistPortrait(artistId: string | undefined): string {
+  const [artistBgUrl, setArtistBgUrl] = useState<string>('');
+  useEffect(() => {
+    setArtistBgUrl('');
+    if (!artistId) return;
+    let cancelled = false;
+    getArtistInfo(artistId).then(info => {
+      if (!cancelled && info.largeImageUrl) setArtistBgUrl(info.largeImageUrl);
+    }).catch(() => {});
+    return () => { cancelled = true; };
+  }, [artistId]);
+  return artistBgUrl;
+}