feat(now-playing): OpenSubsonic playbackReport for live now-playing (#1080)

* feat(now-playing): adopt OpenSubsonic playbackReport for live now-playing

Drive a small playback state machine (starting → playing ↔ paused → stopped)
on the Subsonic-server channel when the server advertises the OpenSubsonic
`playbackReport` extension (Navidrome ≥ 0.62), giving `getNowPlaying` a real
transport state and an extrapolated position. Reports send `ignoreScrobble=true`
so play counts stay on the existing `scrobble.view` 50% path (no double count),
and the effective playback speed is included so the server extrapolates position
correctly with the speed feature on.

- New `playbackReportSession` FSM mirrors the existing `playListenSession`
  lifecycle hooks and is wired at the same player call sites (start / gapless
  switch / queue restore / resume / 15s heartbeat / pause / seek / stop / ended /
  error / app quit). Servers without the extension degrade to the unchanged
  legacy `scrobble.view?submission=false` presence call.
- Gated through the existing serverCapabilities framework: a new
  `FEATURE_PLAYBACK_REPORT` (auto, extension-detected). The OpenSubsonic
  extensions probe now stores the full advertised list once and serves both
  AudioMuse `sonicSimilarity` and `playbackReport` from it, without disturbing
  the legacy Instant Mix opt-in on pre-0.62 servers.
- Now Playing dropdown shows a live position bar and a paused indicator.
- reportPlayback uses the real request params (mediaId / mediaType / positionMs).

Tests: FSM transitions + gating + legacy fallback, capability resolution,
extension-list probe storage/decoupling. Full suite green; no Tauri-boundary
changes.

* feat(now-playing): glide the Live position bar between polls

Extrapolate the position of `playing` entries locally (elapsed × reported
playbackRate from the last 10 s poll) and re-render once a second, so the Live
progress bar advances smoothly instead of jumping on each refresh. Paused and
position-less entries stay frozen. A linear width transition matched to the tick
keeps the fill gliding. Only applies to clients that report a position via the
playbackReport extension.

* fix(now-playing): tighten Live timer layout and report resume immediately

Keep the progress-bar width stable without a wide empty gap before the
timer: reserve ~2ch inside the current-time span only (right-aligned), not
on the whole clock block. Report `playing` to the server as soon as
resume() runs, matching the immediate `paused` report on pause instead of
waiting for the Rust `audio:playing` event.

* docs: CHANGELOG and credits for playbackReport live now-playing (PR #1080)

src/api/subsonic.scheduleProbe.test.ts

@@ -22,6 +22,7 @@ function reset() {
     instantMixProbeByServer: {},
     audiomuseNavidromeByServer: {},
     audiomuseNavidromeIssueByServer: {},
+    openSubsonicExtensionsByServer: {},
   } as never);
 }
 
@@ -57,6 +58,26 @@ describe('scheduleInstantMixProbeForServer (idempotency)', () => {
     scheduleInstantMixProbeForServer(SID, 'url', 'u', 'p', id062);
     expect(fetchMock).toHaveBeenCalledTimes(2);
   });
+
+  it('stores the full extension list and caches both sonicSimilarity and playbackReport', async () => {
+    fetchMock.mockResolvedValue(['sonicSimilarity', 'playbackReport']);
+    scheduleInstantMixProbeForServer(SID, 'url', 'u', 'p', id062);
+    await flush();
+    const s = useAuthStore.getState();
+    expect(s.openSubsonicExtensionsByServer[SID]).toEqual(['sonicSimilarity', 'playbackReport']);
+    expect(s.audiomusePluginProbeByServer[SID]).toBe('present');
+  });
+
+  it('stores the list on a non-Navidrome OpenSubsonic server without driving the AudioMuse probe', async () => {
+    fetchMock.mockResolvedValue(['playbackReport']);
+    const idGonic: SubsonicServerIdentity = { type: 'gonic', serverVersion: '0.16.0', openSubsonic: true };
+    scheduleInstantMixProbeForServer(SID, 'url', 'u', 'p', idGonic);
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+    await flush();
+    const s = useAuthStore.getState();
+    expect(s.openSubsonicExtensionsByServer[SID]).toEqual(['playbackReport']);
+    expect(s.audiomusePluginProbeByServer[SID]).toBeUndefined();
+  });
 });
 
 describe('setSubsonicServerIdentity (version-change cache invalidation)', () => {