refactor(audience-sdk): drop response-body cap on OnError messages

Removes MaxErrorBodyChars (500) and the trim ternary inside
ReadBodyForErrorAsync. The cap was defensive against verbose backend
responses (stack traces, HTML error pages) but the audience backend
returns short structured JSON for both 4xx and 5xx, making the cap
dead code. Consumers now see the full response body verbatim.

Author: ImmutableJeffrey

src/Packages/Audience/Runtime/Transport/HttpTransport.cs

@@ -282,11 +282,6 @@ private static async Task<int> ParseRejectedCount(HttpResponseMessage response)
             }
         }
 
-        // Cap the response-body excerpt the caller sees. Backends sometimes
-        // return verbose stack traces or HTML error pages; trimming keeps
-        // OnError consumers (loggers, UI) from being flooded.
-        private const int MaxErrorBodyChars = 500;
-
         // Best-effort body extraction; null on read failure.
         // Catches narrowed so OOM, OperationCanceledException, and ThreadAbortException
         // propagate — body extraction must not mask process-level faults.
@@ -295,11 +290,7 @@ private static async Task<int> ParseRejectedCount(HttpResponseMessage response)
             try
             {
                 var body = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
-                if (string.IsNullOrWhiteSpace(body)) return null;
-                body = body.Trim();
-                return body.Length > MaxErrorBodyChars
-                    ? body.Substring(0, MaxErrorBodyChars) + "…"
-                    : body;
+                return string.IsNullOrWhiteSpace(body) ? null : body.Trim();
             }
             catch (HttpRequestException) { return null; }
             catch (IOException) { return null; }