Persist talk opinions and pick topics by weight.

A finished circle never set Tick's peopleChanged bit, so people.json kept pre-talk numbers until morning drift. PickTopic compared a 0..total roll to a 0..1 cursor, so gossip almost never changed the subject.

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

src/HSchool.Simulation/TalkCircleSystem.cs

@@ -457,6 +457,7 @@ internal static class TalkCircleSystem
         }
 
         school.TalkCirclesById.Remove(circle.Id);
+        school.RosterTalkDirty = true;
     }
 
     private static bool TryCatchWhisper(School school, ActiveTalkCircle circle)