feat(web): My Wave button, mood picker and endless wave playback (M4)

- WaveButton: TypeScript port of the prototype's canvas animation
  (orb and liquid), breathing at rest, pulsing to the track's BPM and
  energy in the cover palette, following the cursor, pressing with a
  spring; reduced motion and hidden tabs slow or stop it
- home: the wave in the centre with activity and mood chips; changing
  them while playing rebuilds the upcoming tracks without stopping
- player wave mode: asks for the next batch when two tracks are left,
  sends complete / skip / early skip / like / dislike as feedback and
  refreshes the queue right after a reaction or an early skip
- tracks expose bpm, energy and loudness once analysed; library page
  shows analysis progress and 7-day wave metrics; wave style setting

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/core/src/player.ts

@@ -101,6 +101,27 @@ export class PlayQueue {
     return i < 0 ? null : (this.tracks[this.order[i]!] ?? null);
   }
 
+  /** Сколько треков осталось после текущего (без учёта повтора). */
+  get remaining(): number {
+    return Math.max(this.order.length - this.pos - 1, 0);
+  }
+
+  /** Добавить треки в конец (бесконечная волна). */
+  append(tracks: Track[]) {
+    const start = this.tracks.length;
+    this.tracks = [...this.tracks, ...tracks];
+    this.order = [...this.order, ...tracks.map((_, i) => start + i)];
+  }
+
+  /** Убрать ещё не начатые треки после текущего (волна пересобирается после реакции). */
+  dropUpcoming() {
+    const keep = this.order.slice(0, this.pos + 1);
+    const tracks = keep.map((i) => this.tracks[i]!);
+    this.tracks = tracks;
+    this.order = tracks.map((_, i) => i);
+    this.pos = Math.max(tracks.length - 1, 0);
+  }
+
   jump(index: number) {
     const p = this.order.indexOf(index);
     if (p >= 0) this.pos = p;