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.EmulatedEntrypoint/Models/Dtos/Requests/ItemPurchase/ItemPurchasePurchaseRequest.cs

@@ -0,0 +1,22 @@
+using System.Text.Json.Serialization;
+using MessagePack;
+using SVSim.EmulatedEntrypoint.Models.Dtos.Requests;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Requests.ItemPurchase;
+
+/// <summary>
+/// /item_purchase/purchase request body. <c>rest</c> is the client's locally-cached remaining
+/// quota — used as an optional optimistic-concurrency check on the server. Not authoritative;
+/// the server's own counter is canonical.
+/// </summary>
+[MessagePackObject]
+public class ItemPurchasePurchaseRequest : BaseRequest
+{
+    [JsonPropertyName("purchase_id")]
+    [Key("purchase_id")]
+    public int PurchaseId { get; set; }
+
+    [JsonPropertyName("rest")]
+    [Key("rest")]
+    public int Rest { get; set; }
+}

SVSim.EmulatedEntrypoint/Models/Dtos/Responses/ItemPurchase/ItemPurchaseInfoResponse.cs

@@ -0,0 +1,86 @@
+using System.Text.Json.Serialization;
+using MessagePack;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Responses.ItemPurchase;
+
+/// <summary>
+/// /item_purchase/info response.
+/// <para>
+/// <c>item_purchase_info</c> is an array of catalog entries with per-viewer <c>rest</c>
+/// (PurchaseLimit minus the viewer's counter for the relevant period).
+/// </para>
+/// <para>
+/// <c>user_card_pack_ticket_list</c> is the FULL set of card-pack-ticket items (catalog
+/// Items.Type == 2) joined with the viewer's owned counts — even zero counts are emitted, as
+/// the client's parser unconditionally calls <c>PlayerStaticData.UpdateItemNum(item_id, number)</c>
+/// for every entry to refresh its in-memory mapping.
+/// </para>
+/// </summary>
+[MessagePackObject]
+public class ItemPurchaseInfoResponse
+{
+    [JsonPropertyName("item_purchase_info")]
+    [Key("item_purchase_info")]
+    public List<ItemPurchaseEntryDto> ItemPurchaseInfo { get; set; } = new();
+
+    [JsonPropertyName("user_card_pack_ticket_list")]
+    [Key("user_card_pack_ticket_list")]
+    public List<UserCardPackTicketDto> UserCardPackTicketList { get; set; } = new();
+}
+
+[MessagePackObject]
+public class ItemPurchaseEntryDto
+{
+    [JsonPropertyName("purchase_id")]
+    [Key("purchase_id")]
+    public int PurchaseId { get; set; }
+
+    [JsonPropertyName("require_item_type")]
+    [Key("require_item_type")]
+    public int RequireItemType { get; set; }
+
+    [JsonPropertyName("require_item_id")]
+    [Key("require_item_id")]
+    public long RequireItemId { get; set; }
+
+    [JsonPropertyName("require_item_num")]
+    [Key("require_item_num")]
+    public int RequireItemNum { get; set; }
+
+    [JsonPropertyName("purchase_name")]
+    [Key("purchase_name")]
+    public string PurchaseName { get; set; } = string.Empty;
+
+    [JsonPropertyName("purchase_item_type")]
+    [Key("purchase_item_type")]
+    public int PurchaseItemType { get; set; }
+
+    [JsonPropertyName("purchase_item_id")]
+    [Key("purchase_item_id")]
+    public long PurchaseItemId { get; set; }
+
+    [JsonPropertyName("purchase_item_num")]
+    [Key("purchase_item_num")]
+    public int PurchaseItemNum { get; set; }
+
+    /// <summary>0 or 1 — client compares to int 0.</summary>
+    [JsonPropertyName("is_monthly_reset")]
+    [Key("is_monthly_reset")]
+    public int IsMonthlyReset { get; set; }
+
+    [JsonPropertyName("rest")]
+    [Key("rest")]
+    public int Rest { get; set; }
+}
+
+[MessagePackObject]
+public class UserCardPackTicketDto
+{
+    [JsonPropertyName("item_id")]
+    [Key("item_id")]
+    public int ItemId { get; set; }
+
+    [JsonPropertyName("number")]
+    [Key("number")]
+    public int Number { get; set; }
+}

SVSim.EmulatedEntrypoint/Models/Dtos/Responses/ItemPurchase/ItemPurchasePurchaseResponse.cs

@@ -0,0 +1,19 @@
+using System.Text.Json.Serialization;
+using MessagePack;
+using SVSim.EmulatedEntrypoint.Models.Dtos;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Responses.ItemPurchase;
+
+/// <summary>
+/// /item_purchase/purchase response. <c>reward_list</c> uses the standard
+/// <see cref="RewardListEntry"/> shape: post-state totals for currencies, grant counts for
+/// items/cards. First entry is the debit-side post-state for the require_item; subsequent
+/// entries are the grant(s) from RewardGrantService.
+/// </summary>
+[MessagePackObject]
+public class ItemPurchasePurchaseResponse
+{
+    [JsonPropertyName("reward_list")]
+    [Key("reward_list")]
+    public List<RewardListEntry> RewardList { get; set; } = new();
+}