feat(services): declare entitlements + currency-spend primitives

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

SVSim.Database/Services/SpendCurrency.cs

@@ -0,0 +1,16 @@
+namespace SVSim.Database.Services;
+
+/// <summary>The scalar wallet currencies the central debit primitive understands.</summary>
+public enum SpendCurrency { Crystal, Rupee, RedEther, SpotPoint }
+
+public enum SpendOutcome { Success, Insufficient }
+
+/// <summary>
+/// Result of a <see cref="ICurrencySpendService.TrySpendAsync"/> call. <see cref="PostStateTotal"/>
+/// is the balance the client should show after the spend — the real post-deduction balance, or the
+/// freeplay effective balance when the spend was a freeplay no-op.
+/// </summary>
+public sealed record SpendResult(SpendOutcome Outcome, long PostStateTotal)
+{
+    public bool Success => Outcome == SpendOutcome.Success;
+}