feat(core,web): player queue, play events and web player controller (M3, wip)

- core: PlayQueue with shuffle and repeat, PlayAttempt counting only
  time actually played, EventBuffer with batching and backoff, uuidv7
- web: Player over HTMLAudioElement with Media Session, preload of the
  next track, expired-link refresh, local and server playback state,
  hotkeys; PlayerProvider is not wired into the shell yet
- ru/en strings and icons for the player and Collection

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

packages/core/src/player.test.ts

@@ -0,0 +1,110 @@
+import { describe, expect, it, vi } from 'vitest';
+
+import { EventBuffer, PlayAttempt, PlayQueue, uuidv7, type Track } from './player';
+
+const track = (id: string, duration_ms = 200_000): Track => ({
+  id,
+  title: id,
+  duration_ms,
+  artists: [],
+  album: { id: 'a', title: 'A', year: null, cover_url: null, cover_colors: [] },
+  genres: [],
+  disc_no: null,
+  track_no: null,
+  available: true,
+  stream_url: `/s/${id}`,
+  reaction: null,
+});
+
+const ids = (q: PlayQueue) => q.order.map((i) => q.tracks[i]!.id);
+
+describe('PlayQueue', () => {
+  it('walks forward and back, stops at the end', () => {
+    const q = new PlayQueue();
+    q.set([track('a'), track('b'), track('c')], 1);
+    expect(q.current?.id).toBe('b');
+    expect(q.next()?.id).toBe('c');
+    expect(q.peekNext()).toBeNull();
+    expect(q.next()).toBeNull();
+    expect(q.prev()?.id).toBe('b');
+  });
+
+  it('repeats one track only when it ends by itself', () => {
+    const q = new PlayQueue();
+    q.set([track('a'), track('b')]);
+    q.repeat = 'one';
+    expect(q.next(true)?.id).toBe('a');
+    expect(q.next()?.id).toBe('b');
+  });
+
+  it('wraps around with repeat all', () => {
+    const q = new PlayQueue();
+    q.set([track('a'), track('b')], 1);
+    q.repeat = 'all';
+    expect(q.peekNext()?.id).toBe('a');
+    expect(q.next()?.id).toBe('a');
+    expect(q.prev()?.id).toBe('b');
+  });
+
+  it('shuffles keeping the current track first and restores order', () => {
+    let seed = 0.3;
+    const q = new PlayQueue(() => (seed = (seed * 9301 + 0.49297) % 1));
+    q.set(['a', 'b', 'c', 'd', 'e'].map((id) => track(id)), 2);
+    q.setShuffle(true);
+    expect(q.current?.id).toBe('c');
+    expect(ids(q)[0]).toBe('c');
+    expect([...ids(q)].sort()).toEqual(['a', 'b', 'c', 'd', 'e']);
+    q.next();
+    const cur = q.current!.id;
+    q.setShuffle(false);
+    expect(q.current?.id).toBe(cur);
+    expect(ids(q)).toEqual(['a', 'b', 'c', 'd', 'e']);
+  });
+});
+
+describe('PlayAttempt', () => {
+  it('counts only time actually played', () => {
+    const a = new PlayAttempt(track('a'));
+    for (let t = 250; t <= 10_000; t += 250) a.tick(t);
+    expect(a.playedMs).toBe(10_000);
+    expect(a.tick(60_000)).toBe(true); // перемотка вперёд
+    a.tick(60_250);
+    expect(a.playedMs).toBe(10_250);
+    a.seek(5000);
+    a.tick(5250);
+    expect(a.playedMs).toBe(10_500);
+  });
+
+  it('treats the last seconds as finished', () => {
+    const a = new PlayAttempt(track('a', 200_000));
+    expect(a.outcome(196_000)).toBe('play_end');
+    expect(a.outcome(120_000)).toBe('skip');
+  });
+});
+
+describe('EventBuffer', () => {
+  it('sends in batches and retries with backoff', async () => {
+    vi.useFakeTimers();
+    const send = vi.fn().mockRejectedValueOnce(new Error('offline')).mockResolvedValue(undefined);
+    const buf = new EventBuffer({ send }, () => Date.UTC(2026, 0, 1));
+    buf.push({ type: 'play_start', track_id: 't1' });
+    buf.push({ type: 'skip', track_id: 't1', played_ms: 1000 });
+
+    expect(await buf.flush()).toBe(false);
+    expect(buf.pending).toHaveLength(2);
+    await vi.advanceTimersByTimeAsync(2000);
+    expect(send).toHaveBeenCalledTimes(2);
+    expect(buf.pending).toHaveLength(0);
+    const sent = send.mock.calls[1]![0];
+    expect(sent[0].occurred_at).toBe('2026-01-01T00:00:00.000Z');
+    expect(sent[0].id).not.toBe(sent[1].id);
+    vi.useRealTimers();
+  });
+});
+
+describe('uuidv7', () => {
+  it('encodes time and version', () => {
+    const id = uuidv7(0x0190_0000_0000, () => new Uint8Array(16).fill(0xff));
+    expect(id).toMatch(/^01900000-0000-7fff-bfff-ffffffffffff$/);
+  });
+});