feat(item-purchase): /item_purchase/{info,purchase} + catalog

Schema: ItemPurchaseCatalogEntry (single table). Per-viewer quota tracked
via existing ViewerEventCounter keyed by "item_purchase:<id>" with period
JstPeriod.MonthKey when IsMonthlyReset else AllTime.

Controller:
- /info returns catalog + per-period rest (server-computed
  max(0, PurchaseLimit - counter)) + user_card_pack_ticket_list (every
  Items.Type==2 row joined to viewer count, zeros included — client
  unconditionally UpdateItemNum's each entry).
- /purchase: sold_out check before currency check (no counter increment
  on currency failure), inline TryDebit covers RedEther/Crystal/Rupy/Item
  with post-state-total reward_list entry, grant via RewardGrantService.
  Request `rest` accepted but ignored (server counter is canonical).

Importer mirrors PaymentItemImporter shape — idempotent find-or-create,
seed-missing rows preserved. 3 entries from the prod capture.

486 tests pass (was 476; +10 item_purchase tests).

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

SVSim.Bootstrap/Importers/ItemPurchaseImporter.cs

@@ -0,0 +1,59 @@
+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-purchase catalog from <c>seeds/item-purchase.json</c>.
+/// Source is the wire <c>/item_purchase/info</c> response, extracted via
+/// <c>data_dumps/extract/extract-item-purchase.py</c>. Rows missing from the seed are LEFT INTACT.
+/// </summary>
+public class ItemPurchaseImporter
+{
+    public async Task<int> ImportAsync(SVSimDbContext context, string seedDir)
+    {
+        string path = Path.Combine(seedDir, "item-purchase.json");
+        var seed = SeedLoader.LoadList<ItemPurchaseSeed>(path);
+        if (seed.Count == 0)
+        {
+            Console.WriteLine("[ItemPurchaseImporter] No seed rows; skipping.");
+            return 0;
+        }
+
+        var existing = await context.ItemPurchaseCatalog.ToDictionaryAsync(e => e.Id);
+        int created = 0, updated = 0;
+
+        foreach (var s in seed)
+        {
+            if (s.PurchaseId == 0) continue;
+
+            var entry = existing.TryGetValue(s.PurchaseId, out var ex)
+                ? ex : new ItemPurchaseCatalogEntry { Id = s.PurchaseId };
+
+            entry.RequireItemType = s.RequireItemType;
+            entry.RequireItemId = s.RequireItemId;
+            entry.RequireItemNum = s.RequireItemNum;
+            entry.PurchaseItemType = s.PurchaseItemType;
+            entry.PurchaseItemId = s.PurchaseItemId;
+            entry.PurchaseItemNum = s.PurchaseItemNum;
+            entry.PurchaseName = s.PurchaseName;
+            entry.IsMonthlyReset = s.IsMonthlyReset;
+            entry.PurchaseLimit = s.PurchaseLimit;
+            entry.IsEnabled = true;
+
+            if (ex is null)
+            {
+                context.ItemPurchaseCatalog.Add(entry);
+                existing[s.PurchaseId] = entry;
+                created++;
+            }
+            else updated++;
+        }
+
+        await context.SaveChangesAsync();
+        Console.WriteLine($"[ItemPurchaseImporter] +{created}/~{updated}");
+        return created + updated;
+    }
+}