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/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")