Add class-teacher slots on SchoolClass with owner-only assign/clear.

EOF

Co-authored-by: Cursor <cursoragent@cursor.com>

src/HSchool.Simulation/School.cs

@@ -320,6 +320,17 @@ public sealed class School : IDisposable
         TimetableDirty = true;
     }
 
+    /// <summary>
+    /// Writes roster fields that do not change who is in the World (class-teacher slots). No
+    /// respawn and no timetable dirty — unlike <see cref="ApplyStaffing"/>.
+    /// </summary>
+    public void ApplyRosterData(Roster roster)
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        ArgumentNullException.ThrowIfNull(roster);
+        Roster = roster;
+    }
+
     public void SetTimetable(Timetable timetable)
     {
         ObjectDisposedException.ThrowIf(_disposed, this);