feat(svc): IArenaTwoPickService + response DTOs + GetTopAsync

6 response DTOs, IArenaTwoPickService interface + ArenaTwoPickException,
ArenaTwoPickService skeleton with GetTopAsync implemented and stubs for
Tasks 13-15. 3 NUnit tests for GetTopAsync all pass. DI: AddScoped.

SVSim.UnitTests/Services/ArenaTwoPickServiceTopTests.cs

@@ -0,0 +1,87 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using NUnit.Framework;
+using SVSim.Database;
+using SVSim.Database.Models;
+using SVSim.Database.Repositories.Viewer;
+using SVSim.EmulatedEntrypoint.Services;
+using SVSim.UnitTests.Infrastructure;
+
+namespace SVSim.UnitTests.Services;
+
+public class ArenaTwoPickServiceTopTests
+{
+    private static async Task<(SVSimDbContext, IArenaTwoPickRunRepository)> SetupAsync()
+    {
+        var factory = new SVSimTestFactory();
+        var scope = factory.Services.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+        await db.Database.EnsureCreatedAsync();
+        return (db, new ArenaTwoPickRunRepository(db));
+    }
+
+    [Test]
+    public async Task GetTopAsync_returns_null_entry_info_when_no_run()
+    {
+        var (db, runRepo) = await SetupAsync();
+        await using var _ = db;
+        var svc = BuildService(db, runRepo);
+
+        var dto = await svc.GetTopAsync(viewerId: 99);
+        Assert.That(dto.EntryInfo, Is.Null);
+        Assert.That(dto.ClassInfo, Is.Null);
+        Assert.That(dto.DeckInfo, Is.Null);
+    }
+
+    [Test]
+    public async Task GetTopAsync_after_entry_omits_class_info_and_deck_info()
+    {
+        var (db, runRepo) = await SetupAsync();
+        await using var _ = db;
+        await runRepo.UpsertAsync(new ViewerArenaTwoPickRun
+        {
+            ViewerId = 99, EntryId = 1234, RewardScheduleId = 1, ChallengeId = 1,
+            MaxBattleCount = 7, ClassId = 0,
+            CandidateClassIdsJson = "[1,7,8]",
+            CreatedAt = DateTime.UtcNow, UpdatedAt = DateTime.UtcNow,
+        });
+        var svc = BuildService(db, runRepo);
+
+        var dto = await svc.GetTopAsync(viewerId: 99);
+        Assert.That(dto.EntryInfo, Is.Not.Null);
+        Assert.That(dto.EntryInfo!.Id, Is.EqualTo(1234));
+        Assert.That(dto.ClassInfo, Is.Null);
+        Assert.That(dto.DeckInfo, Is.Null);
+        Assert.That(dto.BattleResults!.WinCount, Is.EqualTo(0));
+    }
+
+    [Test]
+    public async Task GetTopAsync_during_card_select_emits_class_and_deck_info()
+    {
+        var (db, runRepo) = await SetupAsync();
+        await using var _ = db;
+        await runRepo.UpsertAsync(new ViewerArenaTwoPickRun
+        {
+            ViewerId = 99, EntryId = 1234, MaxBattleCount = 7, ClassId = 1, LeaderSkinId = 1,
+            CandidateClassIdsJson = "[1,7,8]",
+            SelectTurn = 5, IsSelectCompleted = false,
+            SelectedCardIdsJson = "[100111010,100121010,100131010,100141010,100114010,100124010,100134010,100144010]",
+            CreatedAt = DateTime.UtcNow, UpdatedAt = DateTime.UtcNow,
+        });
+        var svc = BuildService(db, runRepo);
+
+        var dto = await svc.GetTopAsync(viewerId: 99);
+        Assert.That(dto.ClassInfo, Is.Not.Null);
+        Assert.That(dto.ClassInfo!.ClassId1, Is.EqualTo(1));
+        Assert.That(dto.DeckInfo, Is.Not.Null);
+        Assert.That(dto.DeckInfo!.SelectTurn, Is.EqualTo(5));
+        Assert.That(dto.DeckInfo.SelectedCardIds.Count, Is.EqualTo(8));
+    }
+
+    private static IArenaTwoPickService BuildService(SVSimDbContext db, IArenaTwoPickRunRepository runRepo)
+    {
+        // GetTopAsync only uses _runs — every other dep can be null! because the test path
+        // never touches them. The 9th positional arg (db) is required from Task 13 onward.
+        return new ArenaTwoPickService(runRepo, null!, null!, null!, null!, null!, null!, null!, db);
+    }
+}