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/Models/Seed/ItemPurchaseSeed.cs

@@ -0,0 +1,17 @@
+using System.Text.Json.Serialization;
+
+namespace SVSim.Bootstrap.Models.Seed;
+
+public sealed class ItemPurchaseSeed
+{
+    [JsonPropertyName("purchase_id")] public int PurchaseId { get; set; }
+    [JsonPropertyName("require_item_type")] public int RequireItemType { get; set; }
+    [JsonPropertyName("require_item_id")] public long RequireItemId { get; set; }
+    [JsonPropertyName("require_item_num")] public int RequireItemNum { get; set; }
+    [JsonPropertyName("purchase_item_type")] public int PurchaseItemType { get; set; }
+    [JsonPropertyName("purchase_item_id")] public long PurchaseItemId { get; set; }
+    [JsonPropertyName("purchase_item_num")] public int PurchaseItemNum { get; set; }
+    [JsonPropertyName("purchase_name")] public string PurchaseName { get; set; } = "";
+    [JsonPropertyName("is_monthly_reset")] public bool IsMonthlyReset { get; set; }
+    [JsonPropertyName("purchase_limit")] public int PurchaseLimit { get; set; }
+}