Enable WASM response streaming on audio media fetch

Without SetBrowserResponseStreamingEnabled the browser buffers the whole
body before yielding, so the Phase 21.2 read-loop pause backpressured an
already-downloaded payload. Set it on both the initial and seek/refill
requests; safe no-op on the SSR path.

DeepDrftPublic.Client/Clients/TrackMediaClient.cs

@@ -3,6 +3,7 @@ using System.Net.Http.Headers;
 using System.Net.Http.Json;
 using DeepDrftModels.DTOs;
 using DeepDrftModels.Enums;
+using Microsoft.AspNetCore.Components.WebAssembly.Http;
 using Microsoft.Extensions.DependencyInjection;
 using NetBlocks.Models;
 
@@ -79,6 +80,18 @@ public class TrackMediaClient
             using var request = new HttpRequestMessage(HttpMethod.Get, uri);
             request.Headers.Range = new RangeHeaderValue(byteOffset, null);
 
+            // Stream the response body incrementally instead of buffering it whole (Phase 21.4 fix).
+            // In Blazor WebAssembly the HttpClient is backed by the browser fetch API; without this the
+            // browser buffers the ENTIRE body before the response stream yields a byte, so the 21.2
+            // read-loop pause (StreamingAudioPlayerService) backpressures nothing — the whole payload is
+            // already in memory. Enabling streaming makes ReadAsync pull from a browser ReadableStream
+            // whose backpressure reaches the underlying fetch, so pausing reads genuinely throttles the
+            // network. This is a request-option flag, not a runtime call: on the SSR server-to-server path
+            // the SocketsHttpHandler simply ignores the unknown option, so it is safe unguarded. Applies to
+            // BOTH the initial stream (byteOffset 0) and the seek/refill Range requests (21.3) — both share
+            // this method, so both depend on the same backpressure.
+            request.SetBrowserResponseStreamingEnabled(true);
+
             // Use HttpCompletionOption.ResponseHeadersRead to get stream immediately
             var response = await _http.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, cancellationToken);
             response.EnsureSuccessStatusCode();