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/Controls/Settings/SettingsMenu.razor

@@ -1,5 +1,6 @@
 @using DeepDrftPublic.Client.Common
 @using DeepDrftPublic.Client.Controls.Settings
+@using DeepDrftPublic.Client.Services
 
 @*
     The public-site Settings menu (Phase 18 wave 18.6, §4a). An app-bar trigger opening a MudMenu that renders
@@ -31,10 +32,24 @@
 </div>
 
 @code {
+    // The active player, cascaded by AudioPlayerProvider. SettingsMenu sits in the app bar inside the
+    // provider, so it receives the cascade here — but the MudMenu PANEL content below is portaled to
+    // <MudPopoverProvider> (outside the provider), so a cascade cannot reach it. We thread the player into
+    // the setting as an explicit parameter instead: an explicit value captured in the item fragment flows
+    // into portaled content fine, where a [CascadingParameter] would land null.
+    [CascadingParameter] public IStreamingPlayerService? Player { get; set; }
+
     // The settings-item list. Built once; adding a preference is appending one SettingsItem with its control
-    // fragment — the menu body above renders whatever is here without knowing what each item is.
-    private readonly List<SettingsItem> _items =
-    [
-        new SettingsItem("Streaming quality", @<StreamQualitySetting />)
-    ];
+    // fragment — the menu body above renders whatever is here without knowing what each item is. The item
+    // fragment reads Player at render time (when the menu opens), so it picks up the cascaded instance even
+    // though the list itself is initialized before the cascade is set.
+    private readonly List<SettingsItem> _items;
+
+    public SettingsMenu()
+    {
+        _items =
+        [
+            new SettingsItem("Streaming quality", @<StreamQualitySetting Player="@Player" />)
+        ];
+    }
 }