refactor(inventory): move GrantedReward + EffectiveCosmetics into Inventory namespace folder

Both types stay in namespace SVSim.Database.Services so existing using directives
in controllers, services, and tests resolve without change. Their definitions are
extracted to SVSim.Database/Services/Inventory/InventoryGrantTypes.cs; the empty
husks in RewardGrantService.cs and IViewerEntitlements.cs will be deleted in the
next commit.

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

SVSim.Database/Services/IViewerEntitlements.cs

@@ -40,15 +40,3 @@ public interface IViewerEntitlements
     Task<EffectiveCosmetics> EffectiveCosmeticsAsync(Viewer viewer, CancellationToken ct = default);
 }
 
-/// <summary>
-/// Cosmetic projection bundle for /load/index. The four id-lists are "what the viewer owns"
-/// (all of them in freeplay). Leader skins are always the full catalog with a per-skin owned flag;
-/// <see cref="OwnedLeaderSkinIds"/> is every skin id in freeplay.
-/// </summary>
-public sealed record EffectiveCosmetics(
-    IReadOnlyList<int> SleeveIds,
-    IReadOnlyList<int> EmblemIds,
-    IReadOnlyList<int> DegreeIds,
-    IReadOnlyList<int> MyPageBackgroundIds,
-    IReadOnlyList<LeaderSkinEntry> AllLeaderSkins,
-    IReadOnlySet<int> OwnedLeaderSkinIds);