feat(pack): /pack/get_leader_skin_owned_status (empty per-class buckets)

SVSim.UnitTests/Controllers/PackControllerLeaderSkinOwnedStatusTests.cs

@@ -0,0 +1,34 @@
+using System.Net;
+using System.Text;
+using System.Text.Json;
+using NUnit.Framework;
+using SVSim.UnitTests.Infrastructure;
+
+namespace SVSim.UnitTests.Controllers;
+
+public class PackControllerLeaderSkinOwnedStatusTests
+{
+    [Test]
+    public async Task GetLeaderSkinOwnedStatus_returns_nine_empty_buckets()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync(tutorialState: 0);
+        using var client = factory.CreateAuthenticatedClient(viewerId);
+
+        var requestJson = """{"parent_gacha_id":99047,"viewer_id":"0","steam_id":0,"steam_session_ticket":""}""";
+        var response = await client.PostAsync("/pack/get_leader_skin_owned_status",
+            new StringContent(requestJson, Encoding.UTF8, "application/json"));
+
+        Assert.That(response.StatusCode, Is.EqualTo(HttpStatusCode.OK));
+
+        var body = await response.Content.ReadAsStringAsync();
+        using var doc = JsonDocument.Parse(body);
+        // Per spec: keys "0".."8" inclusive, each an empty object.
+        for (int classId = 0; classId <= 8; classId++)
+        {
+            var bucket = doc.RootElement.GetProperty(classId.ToString());
+            Assert.That(bucket.ValueKind, Is.EqualTo(JsonValueKind.Object));
+            Assert.That(bucket.EnumerateObject().Count(), Is.EqualTo(0));
+        }
+    }
+}