perf: remove redundant DiffParser.Parse in ChatMessageItem render

ShouldRenderDiffView already validates the content is a parseable
unified diff. The extra Parse + Count > 0 guard in the render body
was always true when _hasDiffOutput was set, making the else branch
(fallback <pre>) dead code. DiffView internally parses via
OnParametersSet, so the removed call was a wasted parse per render.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: PureWeen

PolyPilot/Components/ChatMessageItem.razor

@@ -233,17 +233,9 @@
                             }
                             else if (_hasDiffOutput)
                             {
-                                var _parsedDiff = DiffParser.Parse(Message.Content);
-                                if (_parsedDiff.Count > 0)
-                                {
-                                    <div class="action-output-diff">
-                                        <DiffView RawDiff="@Message.Content" />
-                                    </div>
-                                }
-                                else
-                                {
-                                    <pre>@ChatMessageList.TruncateResult(Message.Content)</pre>
-                                }
+                                <div class="action-output-diff">
+                                    <DiffView RawDiff="@Message.Content" />
+                                </div>
                             }
                             else if (DiffParser.TryExtractNumberedViewOutput(Message.Content, out var _plainViewOutput))
                             {