Apply stream-quality change live by reloading at current position

Finish the Settings "Apply" behavior so changing streaming quality mid-track
switches format immediately instead of only persisting the cookie for the next
play.

- SettingsMenu reads the AudioPlayerProvider cascade and threads the player into
  StreamQualitySetting as an explicit parameter (the MudMenu panel portals to
  MudPopoverProvider, outside the cascade scope, so a [CascadingParameter] there
  lands null). StreamQualitySetting's Apply persists the cookie, then asks the
  player to reload preserving position.

- Add a "load at timestamp" path to the player rather than restart-from-0-then-
  seek (which audibly played the start and raced the just-started scheduler into
  a crash). ReloadPreservingPositionAsync loads the track in the newly-resolved
  format beginning DIRECTLY at the saved position:
    * new JS resolveStreamOffset(position) resolves the file-absolute byte offset
      with no playback/buffer state (Opus from its sidecar immediately; WAV after
      a header probe),
    * StartFromPositionAsync converges onto the existing seek/refill loop
      (RunSegmentedStreamAsync with a non-null seekPosition) so the decoder
      reinitializes for a header-less Range continuation and starts playback at
      the target,
    * ProbeHeaderAsync feeds the byte-0 segment to the decoder WITHOUT starting
      playback until the WAV header parses (bounded by 256 KB); the probe buffers
      are dropped by the continuation's clearForSeek, so nothing is audible.

- IStreamingPlayerService gains ReloadPreservingPositionAsync; the QueueService
  test fake implements it.

DeepDrftPublic.Client/Services/AudioInteropService.cs

@@ -146,6 +146,18 @@ public class AudioInteropService : IAsyncDisposable
         return await InvokeJsAsync<SeekResult>("DeepDrftAudio.seek", playerId, position);
     }
 
+    /// <summary>
+    /// Resolve the file-absolute byte offset to begin a stream at <paramref name="position"/> with no
+    /// active playback or buffered audio — the "load at timestamp" seam (Phase 18 wave 18.6 format switch).
+    /// Returns <see cref="SeekResult.ByteOffset"/> on success; <see cref="AudioOperationResult.Success"/> is
+    /// false when the decoder cannot yet resolve an offset (e.g. a WAV stream whose header has not been
+    /// parsed), so the caller can feed header bytes and retry.
+    /// </summary>
+    public async Task<SeekResult> ResolveStreamOffsetAsync(string playerId, double position)
+    {
+        return await InvokeJsAsync<SeekResult>("DeepDrftAudio.resolveStreamOffset", playerId, position);
+    }
+
     // New methods for seek-beyond-buffer support
     public async Task<double> GetBufferedDuration(string playerId)
     {