feat(player): Now Playing overlay + synced lyrics panel (A1/A11, §6.7)

Full-screen overlay expanded from the persistent player: big artwork or a
Lyrics tab. Synced (LRC) lyrics highlight the active line by playback position,
auto-scroll, and seek on tap; plain text is the fallback; missing lyrics offers
a re-fetch. Adds lyrics endpoint + LRC parser + isNowPlayingOpen player state.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/store/slices/player.ts

@@ -8,6 +8,7 @@ export interface PlayerState {
   volume: number;
   muted: boolean;
   isQueueOpen: boolean;
+  isNowPlayingOpen: boolean;
 }
 
 export const playerInitialState: PlayerState = {
@@ -18,6 +19,7 @@ export const playerInitialState: PlayerState = {
   volume: 0.78,
   muted: false,
   isQueueOpen: false,
+  isNowPlayingOpen: false,
 };
 
 export const playerSlice = createSlice({
@@ -55,6 +57,12 @@ export const playerSlice = createSlice({
     toggleQueue(state) {
       state.isQueueOpen = !state.isQueueOpen;
     },
+    toggleNowPlaying(state) {
+      state.isNowPlayingOpen = !state.isNowPlayingOpen;
+    },
+    setNowPlayingOpen(state, action: PayloadAction<boolean>) {
+      state.isNowPlayingOpen = action.payload;
+    },
   },
 });
 
@@ -68,5 +76,7 @@ export const {
   setVolume,
   toggleMute,
   toggleQueue,
+  toggleNowPlaying,
+  setNowPlayingOpen,
 } = playerSlice.actions;
 export default playerSlice.reducer;