feat(data): session skills entity, repository, and migration

src/ClaudeDo.Data/Configuration/AppSettingsEntityConfiguration.cs

@@ -44,6 +44,8 @@ public class AppSettingsEntityConfiguration : IEntityTypeConfiguration<AppSettin
         builder.Property(s => s.DailyPrepMaxTasks)
             .HasColumnName("daily_prep_max_tasks").IsRequired().HasDefaultValue(5);
 
+        builder.Property(s => s.SessionSkills).HasColumnName("session_skills");
+
         builder.HasData(new AppSettingsEntity { Id = AppSettingsEntity.SingletonId });
     }
 }