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.Database/Migrations/20260528021818_AddItemPurchaseCatalog.cs

@@ -0,0 +1,45 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace SVSim.Database.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddItemPurchaseCatalog : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "ItemPurchaseCatalog",
+                columns: table => new
+                {
+                    Id = table.Column<int>(type: "integer", nullable: false),
+                    RequireItemType = table.Column<int>(type: "integer", nullable: false),
+                    RequireItemId = table.Column<long>(type: "bigint", nullable: false),
+                    RequireItemNum = table.Column<int>(type: "integer", nullable: false),
+                    PurchaseItemType = table.Column<int>(type: "integer", nullable: false),
+                    PurchaseItemId = table.Column<long>(type: "bigint", nullable: false),
+                    PurchaseItemNum = table.Column<int>(type: "integer", nullable: false),
+                    PurchaseName = table.Column<string>(type: "text", nullable: false),
+                    IsMonthlyReset = table.Column<bool>(type: "boolean", nullable: false),
+                    PurchaseLimit = table.Column<int>(type: "integer", nullable: false),
+                    IsEnabled = table.Column<bool>(type: "boolean", nullable: false),
+                    DateCreated = table.Column<DateTime>(type: "timestamp with time zone", nullable: false),
+                    DateUpdated = table.Column<DateTime>(type: "timestamp with time zone", nullable: true)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_ItemPurchaseCatalog", x => x.Id);
+                });
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(
+                name: "ItemPurchaseCatalog");
+        }
+    }
+}

SVSim.Database/Migrations/SVSimDbContextModelSnapshot.cs

@@ -1107,6 +1107,53 @@ namespace SVSim.Database.Migrations
                     b.ToTable("Items");
                 });
 
+            modelBuilder.Entity("SVSim.Database.Models.ItemPurchaseCatalogEntry", b =>
+                {
+                    b.Property<int>("Id")
+                        .HasColumnType("integer");
+
+                    b.Property<DateTime>("DateCreated")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<DateTime?>("DateUpdated")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<bool>("IsEnabled")
+                        .HasColumnType("boolean");
+
+                    b.Property<bool>("IsMonthlyReset")
+                        .HasColumnType("boolean");
+
+                    b.Property<long>("PurchaseItemId")
+                        .HasColumnType("bigint");
+
+                    b.Property<int>("PurchaseItemNum")
+                        .HasColumnType("integer");
+
+                    b.Property<int>("PurchaseItemType")
+                        .HasColumnType("integer");
+
+                    b.Property<int>("PurchaseLimit")
+                        .HasColumnType("integer");
+
+                    b.Property<string>("PurchaseName")
+                        .IsRequired()
+                        .HasColumnType("text");
+
+                    b.Property<long>("RequireItemId")
+                        .HasColumnType("bigint");
+
+                    b.Property<int>("RequireItemNum")
+                        .HasColumnType("integer");
+
+                    b.Property<int>("RequireItemType")
+                        .HasColumnType("integer");
+
+                    b.HasKey("Id");
+
+                    b.ToTable("ItemPurchaseCatalog");
+                });
+
             modelBuilder.Entity("SVSim.Database.Models.LeaderSkinEntry", b =>
                 {
                     b.Property<int>("Id")

SVSim.Database/Models/ItemPurchaseCatalogEntry.cs

@@ -0,0 +1,39 @@
+using SVSim.Database.Common;
+
+namespace SVSim.Database.Models;
+
+/// <summary>
+/// One row of the /item_purchase/info catalog — an exchange the user can perform N times per
+/// period (monthly or lifetime) by spending <c>RequireItem*</c> to acquire <c>PurchaseItem*</c>.
+/// PK = wire <c>purchase_id</c>.
+/// <para>
+/// Both sides reference <see cref="Enums.UserGoodsType"/>. Captures show the common shape is
+/// currency-for-item (RedEther 5000 → Seer's Globe ×1) or item-for-item (Orb Shard ×5 →
+/// Seer's Globe ×1). Per-viewer remaining quota lives in
+/// <see cref="ViewerEventCounter"/> keyed by <c>"item_purchase:{Id}"</c>.
+/// </para>
+/// </summary>
+public class ItemPurchaseCatalogEntry : BaseEntity<int>
+{
+    public int RequireItemType { get; set; }
+    public long RequireItemId { get; set; }
+    public int RequireItemNum { get; set; }
+
+    public int PurchaseItemType { get; set; }
+    public long PurchaseItemId { get; set; }
+    public int PurchaseItemNum { get; set; }
+
+    /// <summary>
+    /// SystemText-ready display name. May be empty — the client falls back to a templated name
+    /// built from <c>UserGoods.getUserGoodsName + count</c> via SystemText key "Shop_0132".
+    /// </summary>
+    public string PurchaseName { get; set; } = string.Empty;
+
+    /// <summary>True → quota resets at the start of each JST month. False → lifetime quota.</summary>
+    public bool IsMonthlyReset { get; set; }
+
+    /// <summary>Per-period purchase cap. Wire <c>rest</c> = max(0, PurchaseLimit - counter).</summary>
+    public int PurchaseLimit { get; set; }
+
+    public bool IsEnabled { get; set; }
+}

SVSim.Database/SVSimDbContext.cs

@@ -72,6 +72,7 @@ public class SVSimDbContext : DbContext
     public DbSet<BuildDeckProductEntry> BuildDeckProducts => Set<BuildDeckProductEntry>();
     public DbSet<SleeveShopSeriesEntry> SleeveShopSeries => Set<SleeveShopSeriesEntry>();
     public DbSet<SleeveShopProductEntry> SleeveShopProducts => Set<SleeveShopProductEntry>();
+    public DbSet<ItemPurchaseCatalogEntry> ItemPurchaseCatalog => Set<ItemPurchaseCatalogEntry>();
     public DbSet<MaintenanceCardEntry> MaintenanceCards => Set<MaintenanceCardEntry>();
     public DbSet<FeatureMaintenanceEntry> FeatureMaintenances => Set<FeatureMaintenanceEntry>();
     public DbSet<PreReleaseInfo> PreReleaseInfos => Set<PreReleaseInfo>();