Add health condition list, tick, and save for phase 77.

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

src/HSchool.People/Roster.cs

@@ -75,6 +75,12 @@ public sealed record Person
     /// </summary>
     public List<OffenseRecord>? Offenses { get; set; }
 
+    /// <summary>
+    /// Active medical conditions. Null when healthy (empty) so people.json stays compact.
+    /// Needs are not replaced by this list.
+    /// </summary>
+    public List<HealthCondition>? Conditions { get; set; }
+
     public int AgeOn(DateTime asOf) => SchoolYears.AgeYears(BirthDate, asOf);
 }