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")