More story fixes

SVSim.Database/Repositories/Story/StoryMasterRepository.cs

@@ -51,4 +51,15 @@ public class StoryMasterRepository : IStoryMasterRepository
 
     public Task<SpecialBattleSetting?> GetSbsByIdAsync(int sbsId)
         => _db.SpecialBattleSettings.FirstOrDefaultAsync(s => s.Id == sbsId);
+
+    public async Task<StorySubChapter?> FindSubChapterByStoryIdAsync(int storyId)
+    {
+        // StorySubChapter is an owned entity (no DbSet of its own); query through the owning
+        // chapter. SelectMany over the owned collection translates to a JOIN in the relational
+        // provider — no need to materialize the full chapter row.
+        return await _db.StoryChapters
+            .AsNoTracking()
+            .SelectMany(c => c.SubChapters)
+            .FirstOrDefaultAsync(sc => sc.SubChapterStoryId == storyId);
+    }
 }