feat(spot-card-exchange): /spot_card_exchange/{top,exchange} + SpotPoints currency

Final shop family. Schema additions:
- ViewerCurrency.SpotPoints (ulong) — new currency column on Viewers.
- SpotCardExchangeEntry — catalog (distinct from the pre-existing
  SpotCardEntry, which is the /load/index rental-cost concept).
- ViewerSpotCardExchange — standalone composite-PK table tracking
  (viewer, card, exchanged_at, is_pre_release_snapshot). Standalone
  avoids cartesian-explode on viewer-graph reads.

RewardGrantService gains a SpotCardPoint=12 currency case mirroring
the RedEther/Crystal pattern. Doc comment refreshed; SpotCard=11 and
SpotCardOnlyLatestCardPack=13 remain unimplemented with explanatory
NotSupportedException — captures show emitters always use Card=5 with
the spot-card-specific id.

Controller:
- /top: emits exactly 9 clan buckets [{"1": [cards]}, ...] matching
  prod's arbitrary single-key shape. exchange_status per-card (0=
  available, 1=already-exchanged, 2=LimitOver after pre-release cap).
  pre_relase_info WIRE TYPO PRESERVED ("relase" not "release").
- /exchange: server-authoritative price (client-supplied
  exchange_point ignored); debits SpotPoints with post-state-total
  reward_list entry; grants card via RewardGrantService.ApplyAsync
  (cosmetic cascade included); persists ViewerSpotCardExchange row.
  Insufficient points / already-exchanged / pre-release-limit all
  return 400 without partial state.

LoadController now populates /load/index spot_point from
viewer.Currency.SpotPoints (was always 0).

PreReleaseLimit hardcoded to 2 matching capture; promote to GameConfig
when captures show variance.

504 tests pass (was 496; +8 spot-card-exchange tests).

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

SVSim.EmulatedEntrypoint/Models/Dtos/Requests/SpotCardExchange/SpotCardExchangeRequest.cs

@@ -0,0 +1,22 @@
+using System.Text.Json.Serialization;
+using MessagePack;
+using SVSim.EmulatedEntrypoint.Models.Dtos.Requests;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Requests.SpotCardExchange;
+
+/// <summary>
+/// /spot_card_exchange/exchange request — trade <see cref="ExchangePoint"/> spot points for
+/// the card identified by <see cref="CardId"/>. The exchange_point field is the client's view
+/// of the price (sanity-check it against the catalog server-side).
+/// </summary>
+[MessagePackObject]
+public class SpotCardExchangeRequest : BaseRequest
+{
+    [JsonPropertyName("card_id")]
+    [Key("card_id")]
+    public int CardId { get; set; }
+
+    [JsonPropertyName("exchange_point")]
+    [Key("exchange_point")]
+    public int ExchangePoint { get; set; }
+}

SVSim.EmulatedEntrypoint/Models/Dtos/Responses/SpotCardExchange/SpotCardExchangeResponse.cs

@@ -0,0 +1,18 @@
+using System.Text.Json.Serialization;
+using MessagePack;
+using SVSim.EmulatedEntrypoint.Models.Dtos;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Responses.SpotCardExchange;
+
+/// <summary>
+/// /spot_card_exchange/exchange response. <c>reward_list</c> entries follow the standard
+/// shape: SpotCardPoint debit post-state first, then the card grant (with cosmetic cascade
+/// if applicable).
+/// </summary>
+[MessagePackObject]
+public class SpotCardExchangeResponse
+{
+    [JsonPropertyName("reward_list")]
+    [Key("reward_list")]
+    public List<RewardListEntry> RewardList { get; set; } = new();
+}

SVSim.EmulatedEntrypoint/Models/Dtos/Responses/SpotCardExchange/SpotCardExchangeTopResponse.cs

@@ -0,0 +1,88 @@
+using System.Text.Json.Serialization;
+using MessagePack;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Responses.SpotCardExchange;
+
+/// <summary>
+/// /spot_card_exchange/top response.
+/// <para>
+/// <c>exchangeable_card_list</c> is an array of exactly 9 entries indexed by clan id 0..8.
+/// Each entry is a dict keyed by an arbitrary stringified int (prod always emits "1") whose
+/// value is the array of cards for that clan. The client iterates by clan index then dict-keys
+/// (LitJson positional iteration).
+/// </para>
+/// <para>
+/// <c>pre_relase_info</c> — WIRE TYPO PRESERVED ("relase" not "release"). Renaming this field
+/// breaks the client's <c>jsonData["pre_relase_info"]</c> access.
+/// </para>
+/// </summary>
+[MessagePackObject]
+public class SpotCardExchangeTopResponse
+{
+    [JsonPropertyName("spot_point")]
+    [Key("spot_point")]
+    public int SpotPoint { get; set; }
+
+    [JsonPropertyName("exchangeable_card_list")]
+    [Key("exchangeable_card_list")]
+    public List<Dictionary<string, List<SpotCardExchangeCardDto>>> ExchangeableCardList { get; set; } = new();
+
+    /// <summary>Card set id about to cycle out of spot-card eligibility — drives "last chance!" UI.
+    /// Empty string in the captured response. Stays string-typed because the client uses
+    /// <c>int.TryParse</c>.</summary>
+    [JsonPropertyName("soon_cycle_out_card_set_id")]
+    [Key("soon_cycle_out_card_set_id")]
+    public string SoonCycleOutCardSetId { get; set; } = string.Empty;
+
+    [JsonPropertyName("pre_relase_info")]
+    [Key("pre_relase_info")]
+    public PreReleaseInfoDto PreReleaseInfo { get; set; } = new();
+}
+
+[MessagePackObject]
+public class SpotCardExchangeCardDto
+{
+    [JsonPropertyName("card_id")]
+    [Key("card_id")]
+    public long CardId { get; set; }
+
+    /// <summary>SpotCardExchangeInfo.ExchangeStatus — 0=EnableExchange, 1=AlreadyExchange, 2=LimitOver.</summary>
+    [JsonPropertyName("exchange_status")]
+    [Key("exchange_status")]
+    public int ExchangeStatus { get; set; }
+
+    /// <summary>Stringified price — prod ships e.g. "3500", client reads via .ToInt().</summary>
+    [JsonPropertyName("exchange_point")]
+    [Key("exchange_point")]
+    public string ExchangePoint { get; set; } = "0";
+
+    /// <summary>Stringified clan id. Prod ships "0".."8".</summary>
+    [JsonPropertyName("class")]
+    [Key("class")]
+    public string Class { get; set; } = "0";
+
+    [JsonPropertyName("is_pre_release")]
+    [Key("is_pre_release")]
+    public bool IsPreRelease { get; set; }
+
+    /// <summary>Stringified card_set_id this card belongs to.</summary>
+    [JsonPropertyName("ts_rotation_id")]
+    [Key("ts_rotation_id")]
+    public string TsRotationId { get; set; } = "0";
+}
+
+[MessagePackObject]
+public class PreReleaseInfoDto
+{
+    [JsonPropertyName("is_pre_release")]
+    [Key("is_pre_release")]
+    public bool IsPreRelease { get; set; }
+
+    [JsonPropertyName("pre_release_spot_card_exchange_count")]
+    [Key("pre_release_spot_card_exchange_count")]
+    public int PreReleaseSpotCardExchangeCount { get; set; }
+
+    [JsonPropertyName("pre_release_spot_card_exchange_limit")]
+    [Key("pre_release_spot_card_exchange_limit")]
+    public int PreReleaseSpotCardExchangeLimit { get; set; }
+}