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/Services/RewardGrantService.cs

@@ -20,8 +20,9 @@ public sealed record GrantedReward(int RewardType, long RewardId, int RewardNum)
 ///
 /// <para>
 /// <b>DO NOT reimplement reward dispatch in a controller or new helper.</b> This service handles
-/// RedEther, Crystal, Item, Card (with <see cref="CardCosmeticReward"/> cascade), Sleeve, Emblem,
-/// Degree, Rupy, Skin, MyPageBG — everything except SpotCard (TODO). Endpoint code that takes a
+/// RedEther, Crystal, SpotCardPoint, Item, Card (with <see cref="CardCosmeticReward"/> cascade),
+/// Sleeve, Emblem, Degree, Rupy, Skin, MyPageBG — everything except the dead-letter SpotCard /
+/// SpotCardOnlyLatestCardPack slots (use Card=5 instead). Endpoint code that takes a
 /// list of <c>(type, id, num)</c> tuples should iterate and call <see cref="ApplyAsync"/>
 /// per tuple — never switch on type yourself, never filter to "only card-typed rewards", never
 /// build a second dispatch table. Past duplicate implementations (ICardAcquisitionService in the
@@ -87,6 +88,10 @@ public sealed class RewardGrantService
                 viewer.Currency.RedEther += (ulong)num;
                 return Single(type, detailId, checked((int)viewer.Currency.RedEther));
 
+            case UserGoodsType.SpotCardPoint:
+                viewer.Currency.SpotPoints += (ulong)num;
+                return Single(type, detailId, checked((int)viewer.Currency.SpotPoints));
+
             case UserGoodsType.Item:
             {
                 var owned = viewer.Items.FirstOrDefault(i => i.Item.Id == (int)detailId);
@@ -106,11 +111,11 @@ public sealed class RewardGrantService
 
             case UserGoodsType.SpotCard:
             case UserGoodsType.SpotCardOnlyLatestCardPack:
-                // TODO: spot cards are currently global in our seed data; the existence of these
-                // reward types suggests there's a mix of global + per-player spot cards. Revisit
-                // when per-player spot-card infrastructure lands.
+                // Spot-card-typed grants don't appear in captures — emitters always use Card=5
+                // with the spot-card-specific id. These two enum slots remain unimplemented; if a
+                // capture ever shows one in a reward_list we'll know to wire them up here.
                 throw new NotSupportedException(
-                    $"{type} rewards are not yet supported — see SpotCard TODO in RewardGrantService.");
+                    $"{type} rewards are not yet supported — emitters use Card=5 instead.");
 
             default:
                 throw new NotSupportedException($"UserGoodsType {type} not yet handled by RewardGrantService");