feat(packs): split TryGetFoilTwin into ICardFoilLookup

Extracts the foil-twin lookup from ICardPoolProvider into a dedicated
ICardFoilLookup service. PackOpenService takes the lookup as a
parameter; the legacy DbCardPoolProvider stays registered until T12
removes it.

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

SVSim.EmulatedEntrypoint/Services/DbCardFoilLookup.cs

@@ -0,0 +1,13 @@
+using SVSim.Database;
+using SVSim.Database.Models;
+
+namespace SVSim.EmulatedEntrypoint.Services;
+
+public class DbCardFoilLookup : ICardFoilLookup
+{
+    private readonly SVSimDbContext _db;
+    public DbCardFoilLookup(SVSimDbContext db) { _db = db; }
+
+    public ShadowverseCardEntry? TryGetFoilTwin(long baseCardId) =>
+        _db.Cards.FirstOrDefault(c => c.Id == baseCardId + 1 && c.IsFoil);
+}