Revert "test(site): admit one heavy website child per logical processor"

This reverts commit fb566eb. With four admitted heavy children on the
4-vCPU runner, the shared isolated projection fixture exceeded its
300-second process deadline in Website run 40488439737; 52 tests that
await that fixture failed with TaskCanceledException at about 4m59s and
the coverage gate failed as a consequence. The children contend for
memory and disk as well as CPU, so the processor-count capacity was a
wrong diagnosis; capacity 2 is restored.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: KSemenenko

tests/KeyLoad.WebsiteTests/Configuration/SiteExecutionOptions.cs

@@ -21,7 +21,6 @@ internal sealed class SiteExecutionOptions
     public TimeSpan IsolatedProcessDeadline { get; set; } = TimeSpan.FromSeconds(300);
     public int BrowserSessionCapacity { get; set; } = 1;
     public int MaximumQueued { get; set; } = 64;
-    // Heavy Node children are single-threaded; one admitted child per logical processor keeps every core busy.
-    public int HeavyChildCapacity { get; set; } = Environment.ProcessorCount;
+    public int HeavyChildCapacity { get; set; } = 2;
     public int ProcessOutputBufferCharacters { get; set; } = 4096;
 }