refactor(arena-tk2): FinishAsync returns RunFinishOutcome with WasFullClear signal

Introduces RunFinishOutcome — a semantic record that wraps the wire
FinishResponseDto with the controller-side WasFullClear signal used to fire
the challenge_full_clear mission event. The wire response isn't affected
(controller unwraps the .Response field before returning to the client);
RetireAsync stays returning FinishResponseDto because retire cannot full-clear.

Full-clear detection compares run.WinCount against ResolveMaxBattleCountAsync
rather than hard-coding 5, so a future TK2 rules-config change tracks
automatically. New test covers the full-clear signal explicitly.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.EmulatedEntrypoint/Models/Dtos/Responses/ArenaTwoPick/RunFinishOutcome.cs

@@ -0,0 +1,9 @@
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Responses.ArenaTwoPick;
+
+/// <summary>
+/// What <see cref="Services.IArenaTwoPickService.FinishAsync(long)"/> returns to
+/// <c>ArenaTwoPickController.Finish</c>. The wire response is <see cref="Response"/>;
+/// <see cref="WasFullClear"/> is a controller-side signal for the
+/// <c>challenge_full_clear</c> mission emit and is never serialized.
+/// </summary>
+public sealed record RunFinishOutcome(FinishResponseDto Response, bool WasFullClear);