Add lesson whispers, teacher catch chance, and after-bell teacher talk.

Whispering cuts lesson skill gain from BehaviorDef; a teacher in the room may interrupt into a discipline circle, and pedagogy scales the pupil's opinion of the teacher.

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

src/HSchool.People/Seed.cs

@@ -17,6 +17,7 @@ public static class Seed
     public const int NativeLanguageSalt = 9;
     public const int ClimatePresetSalt = 10;
     public const int ApparelSalt = 11;
+    public const int WhisperSalt = 12;
 
     /// <summary>A stream that belongs to the school rather than to one family.</summary>
     public static int ForSchool(int schoolSeed, int salt) => Mix(schoolSeed, familyIndex: -1, salt);