feat(bootstrap): ArenaTwoPickRewardImporter + tests

Idempotent upsert importer for arena-two-pick-rewards.json; 2 NUnit tests
(16-row load + idempotency). Wired into Program.cs globals pipeline after
ArenaSeasonImporter.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SVSim.UnitTests/Importers/ArenaTwoPickRewardImporterTests.cs

@@ -0,0 +1,62 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using SVSim.Bootstrap.Importers;
+using SVSim.Database;
+using SVSim.UnitTests.Infrastructure;
+
+namespace SVSim.UnitTests.Importers;
+
+public class ArenaTwoPickRewardImporterTests
+{
+    private static async Task<SVSimDbContext> CreateContextAsync()
+    {
+        var factory = new SVSimTestFactory();
+        var scope = factory.Services.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+        await db.Database.EnsureCreatedAsync();
+        return db;
+    }
+
+    [Test]
+    public async Task Import_loads_all_16_rows_from_seed_file()
+    {
+        await using var db = await CreateContextAsync();
+        var importer = new ArenaTwoPickRewardImporter();
+
+        await importer.ImportAsync(db, FindSeedDir());
+
+        var rows = await db.ArenaTwoPickRewards.OrderBy(r => r.WinCount).ThenBy(r => r.RewardType).ToListAsync();
+        Assert.That(rows.Count, Is.EqualTo(16));
+        Assert.That(rows.Max(r => r.WinCount), Is.EqualTo(7));
+
+        var w0 = rows.Where(r => r.WinCount == 0).ToList();
+        Assert.That(w0.Count, Is.EqualTo(2));
+        Assert.That(w0.Single(r => r.RewardType == 4).RewardNum, Is.EqualTo(1));
+        Assert.That(w0.Single(r => r.RewardType == 9).RewardNum, Is.EqualTo(100));
+
+        var w7 = rows.Where(r => r.WinCount == 7).ToList();
+        Assert.That(w7.Single(r => r.RewardType == 4).RewardNum, Is.EqualTo(2));
+        Assert.That(w7.Single(r => r.RewardType == 9).RewardNum, Is.EqualTo(1500));
+    }
+
+    [Test]
+    public async Task Import_is_idempotent_on_re_run()
+    {
+        await using var db = await CreateContextAsync();
+        var importer = new ArenaTwoPickRewardImporter();
+
+        await importer.ImportAsync(db, FindSeedDir());
+        await importer.ImportAsync(db, FindSeedDir());
+
+        var count = await db.ArenaTwoPickRewards.CountAsync();
+        Assert.That(count, Is.EqualTo(16), "second import should upsert, not duplicate");
+    }
+
+    private static string FindSeedDir()
+    {
+        var dir = Path.Combine(AppContext.BaseDirectory, "Data", "seeds");
+        if (!Directory.Exists(dir))
+            throw new DirectoryNotFoundException($"seeds dir not found at {dir} — verify csproj copy");
+        return dir;
+    }
+}