test(entitlements): cover EffectiveOwnedCards/Cosmetics; document include preconditions

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

SVSim.Database/Services/IViewerEntitlements.cs

@@ -8,6 +8,14 @@ namespace SVSim.Database.Services;
 /// Freeplay flag; all freeplay read-side behavior lives here. See
 /// docs/superpowers/specs/2026-05-29-freeplay-mode-design.md.
 /// </summary>
+/// <remarks>
+/// <b>Include precondition:</b> methods that inspect the viewer's collections require the
+/// viewer to have been loaded with <c>.Include(v =&gt; v.Cards).ThenInclude(c =&gt; c.Card)</c>
+/// and the cosmetic collections
+/// (<c>Sleeves</c>, <c>Emblems</c>, <c>Degrees</c>, <c>LeaderSkins</c>, <c>MyPageBackgrounds</c>)
+/// included. Without those includes the EF owned-collection nav refs are null or zero-filled
+/// (see the EF owned-collection nav-include pitfall in MEMORY.md).
+/// </remarks>
 public interface IViewerEntitlements
 {
     /// <summary>True when the global Freeplay config section is enabled.</summary>