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/Importers/ItemImporter.cs

@@ -0,0 +1,52 @@
+using Microsoft.EntityFrameworkCore;
+using SVSim.Bootstrap.Models.Seed;
+using SVSim.Database;
+using SVSim.Database.Models;
+
+namespace SVSim.Bootstrap.Importers;
+
+/// <summary>
+/// Idempotent upsert of the item catalog from <c>seeds/items.json</c>. Source is the client's
+/// <c>item_master.csv</c> + <c>itemtext.json</c> (extracted via
+/// <c>data_dumps/extract/extract-items.py</c>). Rows missing from the seed are LEFT INTACT.
+/// </summary>
+public class ItemImporter
+{
+    public async Task<int> ImportAsync(SVSimDbContext context, string seedDir)
+    {
+        string path = Path.Combine(seedDir, "items.json");
+        var seed = SeedLoader.LoadList<ItemSeed>(path);
+        if (seed.Count == 0)
+        {
+            Console.WriteLine("[ItemImporter] No seed rows; skipping.");
+            return 0;
+        }
+
+        var existing = await context.Items.ToDictionaryAsync(e => e.Id);
+        int created = 0, updated = 0;
+
+        foreach (var s in seed)
+        {
+            if (s.ItemId == 0) continue;
+
+            var entry = existing.TryGetValue(s.ItemId, out var ex)
+                ? ex : new ItemEntry { Id = s.ItemId };
+
+            entry.Name = s.Name;
+            entry.Type = s.Type;
+            entry.ThumbnailPath = s.ThumbnailPath;
+
+            if (ex is null)
+            {
+                context.Items.Add(entry);
+                existing[s.ItemId] = entry;
+                created++;
+            }
+            else updated++;
+        }
+
+        await context.SaveChangesAsync();
+        Console.WriteLine($"[ItemImporter] +{created}/~{updated}");
+        return created + updated;
+    }
+}