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/Migrations/SVSimDbContextModelSnapshot.cs

@@ -2206,6 +2206,40 @@ namespace SVSim.Database.Migrations
                     b.ToTable("SpotCards");
                 });
 
+            modelBuilder.Entity("SVSim.Database.Models.SpotCardExchangeEntry", b =>
+                {
+                    b.Property<long>("Id")
+                        .HasColumnType("bigint");
+
+                    b.Property<long>("CardId")
+                        .HasColumnType("bigint");
+
+                    b.Property<int>("ClassId")
+                        .HasColumnType("integer");
+
+                    b.Property<DateTime>("DateCreated")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<DateTime?>("DateUpdated")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<int>("ExchangePoint")
+                        .HasColumnType("integer");
+
+                    b.Property<bool>("IsEnabled")
+                        .HasColumnType("boolean");
+
+                    b.Property<bool>("IsPreRelease")
+                        .HasColumnType("boolean");
+
+                    b.Property<long>("TsRotationId")
+                        .HasColumnType("bigint");
+
+                    b.HasKey("Id");
+
+                    b.ToTable("SpotCardExchangeCatalog");
+                });
+
             modelBuilder.Entity("SVSim.Database.Models.UnlimitedRestrictionEntry", b =>
                 {
                     b.Property<long>("Id")
@@ -2473,6 +2507,27 @@ namespace SVSim.Database.Migrations
                     b.ToTable("ViewerPuzzleClears");
                 });
 
+            modelBuilder.Entity("SVSim.Database.Models.ViewerSpotCardExchange", b =>
+                {
+                    b.Property<long>("ViewerId")
+                        .HasColumnType("bigint");
+
+                    b.Property<long>("CardId")
+                        .HasColumnType("bigint");
+
+                    b.Property<DateTime>("ExchangedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<bool>("IsPreRelease")
+                        .HasColumnType("boolean");
+
+                    b.HasKey("ViewerId", "CardId");
+
+                    b.HasIndex("ViewerId");
+
+                    b.ToTable("ViewerSpotCardExchanges");
+                });
+
             modelBuilder.Entity("SleeveEntryViewer", b =>
                 {
                     b.Property<int>("SleevesId")
@@ -3390,6 +3445,9 @@ namespace SVSim.Database.Migrations
                             b1.Property<decimal>("Rupees")
                                 .HasColumnType("numeric(20,0)");
 
+                            b1.Property<decimal>("SpotPoints")
+                                .HasColumnType("numeric(20,0)");
+
                             b1.Property<decimal>("SteamCrystals")
                                 .HasColumnType("numeric(20,0)");