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/Services/IArenaTwoPickService.cs

@@ -9,7 +9,12 @@ public interface IArenaTwoPickService
     Task<ClassChooseResponseDto> ChooseClassAsync(long viewerId, int classId);
     Task<CardChooseResponseDto> ChooseCardAsync(long viewerId, long selectedId);
     Task<FinishResponseDto> RetireAsync(long viewerId);
-    Task<FinishResponseDto> FinishAsync(long viewerId);
+    /// <summary>
+    /// Ends a completed TK2 run (5 battles played) and grants the reward tier for
+    /// <c>run.WinCount</c>. Returns both the wire-shape rewards and a controller-side
+    /// signal for mission emit (<see cref="RunFinishOutcome.WasFullClear"/>).
+    /// </summary>
+    Task<RunFinishOutcome> FinishAsync(long viewerId);
     Task<BattleFinishResultDto> RecordBattleResultAsync(long viewerId, bool isWin);
 }