feat(leader-skin): shop catalog + 5 endpoints (/products, /buy, /buy_set, /buy_set_item, /ids)

Schema: LeaderSkinShopSeries -> Products (owned rewards) + owned
SetCompletionRewards on the series; ViewerLeaderSkinSetClaim composite
PK (ViewerId, SeriesId) backs the /buy_set_item idempotent-claim check.

Importer mirrors SleeveShopImporter: idempotent find-or-create, owned
collections rewritten wholesale on rerun. 16 series, 104 products.

Controller (extends existing /set with 5 new endpoints):
- /products: dict-keyed-by-series_id-string wire shape. is_completed
  per-viewer, rewards.status from ViewerLeaderSkinSetClaim (0=no set
  sale, 1=available, 2=claimed) matching client RewardStatus enum.
- /buy: single skin, sales_type 1/2 dispatch, 3=>501.
- /buy_set: whole series at SetPrice; requires set_sales_status != 0;
  grants every product's rewards (RewardGrantService idempotent on
  already-owned cosmetics, so partial-set buys don't double-add).
- /buy_set_item: requires viewer owns every skin in series; idempotent
  on re-claim (returns 200 + empty reward_list, not 400) so client
  retries don't error.
- /ids: flat owned-skin-id list for badge refresh.

496 tests pass (was 486; +10 leader-skin-shop tests).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.EmulatedEntrypoint/Models/Dtos/Requests/LeaderSkin/LeaderSkinBuyRequest.cs

@@ -0,0 +1,26 @@
+using System.Text.Json.Serialization;
+using MessagePack;
+using SVSim.EmulatedEntrypoint.Models.Dtos.Requests;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Requests.LeaderSkin;
+
+/// <summary>
+/// /leader_skin/buy request body. sales_type is ShopCommonUtility.SalesType:
+/// 0=free, 1=crystal, 2=rupy, 3=ticket (v1: 3 returns 501 — no ticket-priced skin captured).
+/// <see cref="ItemId"/> is the ticket item id when paying with a ticket, null otherwise.
+/// </summary>
+[MessagePackObject]
+public class LeaderSkinBuyRequest : BaseRequest
+{
+    [JsonPropertyName("product_id")]
+    [Key("product_id")]
+    public int ProductId { get; set; }
+
+    [JsonPropertyName("sales_type")]
+    [Key("sales_type")]
+    public int SalesType { get; set; }
+
+    [JsonPropertyName("item_id")]
+    [Key("item_id")]
+    public long? ItemId { get; set; }
+}

SVSim.EmulatedEntrypoint/Models/Dtos/Requests/LeaderSkin/LeaderSkinBuySetItemRequest.cs

@@ -0,0 +1,18 @@
+using System.Text.Json.Serialization;
+using MessagePack;
+using SVSim.EmulatedEntrypoint.Models.Dtos.Requests;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Requests.LeaderSkin;
+
+/// <summary>
+/// /leader_skin/buy_set_item — claim the series-completion bonus once every skin in the series
+/// is owned. <c>sales_type</c> field exists on the client's param class but is never set; server
+/// ignores it.
+/// </summary>
+[MessagePackObject]
+public class LeaderSkinBuySetItemRequest : BaseRequest
+{
+    [JsonPropertyName("series_id")]
+    [Key("series_id")]
+    public int SeriesId { get; set; }
+}

SVSim.EmulatedEntrypoint/Models/Dtos/Requests/LeaderSkin/LeaderSkinBuySetRequest.cs

@@ -0,0 +1,24 @@
+using System.Text.Json.Serialization;
+using MessagePack;
+using SVSim.EmulatedEntrypoint.Models.Dtos.Requests;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Requests.LeaderSkin;
+
+/// <summary>
+/// /leader_skin/buy_set — purchase every skin in a series in one call (cheaper per-skin).
+/// </summary>
+[MessagePackObject]
+public class LeaderSkinBuySetRequest : BaseRequest
+{
+    [JsonPropertyName("series_id")]
+    [Key("series_id")]
+    public int SeriesId { get; set; }
+
+    [JsonPropertyName("sales_type")]
+    [Key("sales_type")]
+    public int SalesType { get; set; }
+
+    [JsonPropertyName("item_id")]
+    [Key("item_id")]
+    public long? ItemId { get; set; }
+}