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.Database/Models/SpotCardExchangeEntry.cs

@@ -0,0 +1,30 @@
+using SVSim.Database.Common;
+
+namespace SVSim.Database.Models;
+
+/// <summary>
+/// One catalog entry of the /spot_card_exchange/top shop — a card the viewer can buy with
+/// spot points. PK = wire card_id. Distinct from <see cref="SpotCardEntry"/> (which is the
+/// /load/index data.spot_cards rental-cost list — a different concept).
+/// <para>
+/// <see cref="TsRotationId"/> matches the card_set_id; cards cycle out of the exchange when
+/// their set rotates. <see cref="IsPreRelease"/> distinguishes the pre-release-pool subset
+/// gated by <c>pre_release_spot_card_exchange_limit</c>.
+/// </para>
+/// </summary>
+public class SpotCardExchangeEntry : BaseEntity<long>
+{
+    public long CardId { get => Id; set => Id = value; }
+
+    /// <summary>Wire <c>class</c> field — clan id (0=Neutral, 1=Forestcraft, ..., 8).</summary>
+    public int ClassId { get; set; }
+
+    public int ExchangePoint { get; set; }
+
+    /// <summary>Wire <c>ts_rotation_id</c> — card_set_id this card belongs to.</summary>
+    public long TsRotationId { get; set; }
+
+    public bool IsPreRelease { get; set; }
+
+    public bool IsEnabled { get; set; }
+}

SVSim.Database/Models/ViewerCurrency.cs

@@ -14,4 +14,11 @@ public class ViewerCurrency
     public ulong LifeTotalCrystals { get; set; }
     public ulong RedEther { get; set; }
     public ulong Rupees { get; set; }
+
+    /// <summary>
+    /// Spot card points — currency earned from battles/missions, spent at /spot_card_exchange/exchange.
+    /// Wire field <c>spot_point</c> in /load/index and /spot_card_exchange/top; reward_type 12
+    /// (<see cref="Enums.UserGoodsType.SpotCardPoint"/>) in reward_list entries.
+    /// </summary>
+    public ulong SpotPoints { get; set; }
 }

SVSim.Database/Models/ViewerSpotCardExchange.cs

@@ -0,0 +1,16 @@
+namespace SVSim.Database.Models;
+
+/// <summary>
+/// One row per (viewer, exchanged card). Composite PK (ViewerId, CardId). Standalone table
+/// (not a Viewer owned collection) to avoid cartesian-explode on viewer-graph reads.
+/// <see cref="IsPreRelease"/> snapshot at exchange time so the pre-release counter can be
+/// computed without joining back to <see cref="SpotCardExchangeEntry"/> (and to survive
+/// catalog edits that re-classify a card).
+/// </summary>
+public class ViewerSpotCardExchange
+{
+    public long ViewerId { get; set; }
+    public long CardId { get; set; }
+    public bool IsPreRelease { get; set; }
+    public DateTime ExchangedAt { get; set; }
+}