feat(repo): GetStoryDecksByClass joins story-deck presentation to product card lists

Adds StoryDeckView projection, IBuildDeckRepository.GetStoryDecksByClass interface method,
and BuildDeckRepository implementation that loads StoryDeckEntry rows for a class, fetches
matching BuildDeckProductEntry card lists, and expands each card by Number into a flat
CardIdArray. TDD: 2 tests in StoryDeckRepositoryTests (expand + empty-class).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SVSim.Database/Repositories/BuildDeck/StoryDeckView.cs

@@ -0,0 +1,22 @@
+using SVSim.Database.Enums;
+
+namespace SVSim.Database.Repositories.BuildDeck;
+
+/// <summary>
+/// A story-select deck ready for the wire: presentation metadata from StoryDeckEntry plus the
+/// 40-card list expanded from the matching BuildDeckProductEntry. Plain projection, not an entity.
+/// </summary>
+public sealed class StoryDeckView
+{
+    public int DeckNo { get; init; }
+    public StoryDeckKind Kind { get; init; }
+    public int ClassId { get; init; }
+    public string DeckName { get; init; } = string.Empty;
+    public int SleeveId { get; init; }
+    public int LeaderSkinId { get; init; }
+    public int IsRecommend { get; init; }
+    public int OrderNum { get; init; }
+    public int EntryNo { get; init; }
+    public int? DeckFormat { get; init; }
+    public List<long> CardIdArray { get; init; } = new();
+}