feat(items): catalog import with Type + ThumbnailPath columns

ItemEntry gains Type (client item_type enum, 1=challenge, 2=card-pack
ticket, 3=premium orb, 4=colosseum, 5=orb piece, 6=skin/event ticket,
7=other) and ThumbnailPath. ItemImporter mirrors PaymentItemImporter
shape: find-or-create per item_id, save once, idempotent. Wired into
Bootstrap.Program and SVSimTestFactory.SeedGlobalsAsync. Unblocks
/item_purchase/info (filters card-pack tickets by Type==2) and any
reward grant of UserGoodsType.Item, which previously threw because
the catalog was empty.

466 tests pass (was 461).

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

SVSim.Bootstrap/Models/Seed/ItemSeed.cs

@@ -0,0 +1,11 @@
+using System.Text.Json.Serialization;
+
+namespace SVSim.Bootstrap.Models.Seed;
+
+public sealed class ItemSeed
+{
+    [JsonPropertyName("item_id")] public int ItemId { get; set; }
+    [JsonPropertyName("name")] public string Name { get; set; } = "";
+    [JsonPropertyName("type")] public int Type { get; set; }
+    [JsonPropertyName("thumbnail_path")] public string ThumbnailPath { get; set; } = "";
+}