feat(entitlement): pivot to paid app ownership

Check Steam ownership of the paid app with BIsSubscribedApp; keep Debug fake ownership out of Release. Ref: https://partner.steamgames.com/doc/api/ISteamApps#BIsSubscribedApp

Services/Entitlement/IEntitlement.cs

@@ -1,19 +1,12 @@
 namespace ytLive.Services.Entitlement;
 
 /// <summary>
-/// Where "is this copy licensed for Pro output?" comes from.
+/// Whether the current Steam account owns the paid app.
 ///
-/// <para><b>One question, two sources.</b> The lifetime SKU is a Steam DLC; the monthly is a Polar
-/// lease. Both answer this interface, and everything downstream — the output profile, the greyed
-/// tier list, the notices — reads only this. Nothing outside <c>Services/Entitlement</c> may know
-/// which rail proved it.</para>
-///
-/// <para><b>Fail closed.</b> An implementation that cannot reach its source, cannot load its
-/// native library, or has no product id configured returns <c>false</c>. Pro is never a default,
-/// never a cached "probably", and never the result of an exception being swallowed as true.</para>
+/// <para>Steam is the source of truth. Failure to reach Steam, load its native library, or
+/// resolve the paid app ID returns <c>false</c>.</para>
 /// </summary>
 public interface IEntitlement
 {
-    /// <summary>True when this session may emit above the free output budget.</summary>
-    bool IsPro { get; }
+    bool IsAppOwned { get; }
 }