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/store/playTrackAction.ts

@@ -1,4 +1,4 @@
-import { reportNowPlaying } from '../api/subsonicScrobble';
+import { playbackReportStart } from './playbackReportSession';
 import { invoke } from '@tauri-apps/api/core';
 import { getMusicNetworkRuntimeOrNull } from '../music-network';
 import { setDeferHotCachePrefetch } from '../utils/cache/hotCacheGate';
@@ -413,10 +413,11 @@ export function runPlayTrack(
         }, 500);
       });
 
-    // Navidrome now-playing follows nowPlayingEnabled; Music Network now-playing
-    // follows scrobbling, as Last.fm now-playing did (runtime gates internally).
-    const { nowPlayingEnabled: npEnabled } = useAuthStore.getState();
-    if (npEnabled) reportNowPlaying(scopedTrack.id, playbackSid);
+    // Subsonic-server now-playing follows nowPlayingEnabled; Music Network
+    // now-playing follows scrobbling, as Last.fm now-playing did (runtime gates
+    // internally). playbackReportStart opens the live FSM on extension-capable
+    // servers and falls back to the legacy presence call otherwise.
+    playbackReportStart(scopedTrack.id, playbackSid);
     const runtime = getMusicNetworkRuntimeOrNull();
     void runtime?.dispatchNowPlaying({
       title: scopedTrack.title,