feat(rank): viewer repo LoadForRankProgressAsync

Split-query load of Classes (for class XP) + RankProgress (for rank grant)
so RankBattleController.Finish uses a single viewer read. Test factory's
ReferenceDataImporter.ImportAllAsync already seeds RankInfo — no test
helper needed.

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

SVSim.Database/Repositories/Viewer/IViewerRepository.cs

@@ -59,6 +59,14 @@ public interface IViewerRepository
     /// </summary>
     Task<Models.Viewer?> LoadForBattleXpGrantAsync(long viewerId, CancellationToken ct = default);
 
+    /// <summary>
+    /// Load a viewer with the joins <see cref="Controllers.RankBattleController"/>'s <c>Finish</c>
+    /// needs: Classes (for the class-XP grant) + RankProgress (for the rank grant). Split-query
+    /// per <c>project_ef_split_query</c> to avoid the cartesian explosion when both nav
+    /// collections are populated on the same viewer.
+    /// </summary>
+    Task<Models.Viewer?> LoadForRankProgressAsync(long viewerId, CancellationToken ct = default);
+
     /// <summary>Sets Viewer.GuildId to <paramref name="guildId"/>. No-op if the viewer does not exist.</summary>
     Task SetGuildIdAsync(long viewerId, int guildId, CancellationToken ct = default);