feat(bp): IBattlePassService skeleton + level-curve method + DI

SVSim.EmulatedEntrypoint/Services/IBattlePassService.cs

@@ -0,0 +1,11 @@
+using SVSim.EmulatedEntrypoint.Models.Dtos;
+
+namespace SVSim.EmulatedEntrypoint.Services;
+
+public interface IBattlePassService
+{
+    /// <summary>Global level curve as wire-string dictionary; null if no levels seeded.</summary>
+    Task<IReadOnlyDictionary<string, BattlePassLevel>?> GetLevelCurveAsync(CancellationToken ct);
+
+    // The Info / ItemList / Buy / AddPoints methods are added in later tasks (11, 12, 13, 14).
+}