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

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

src/HSchool.Simulation/HealthConditionSystem.cs

@@ -0,0 +1,26 @@
+using HSchool.People;
+
+namespace HSchool.Simulation;
+
+/// <summary>
+/// Ticks medical condition severity on the roster. Contagion and DiseaseDef outbreaks are later phases.
+/// </summary>
+internal static class HealthConditionSystem
+{
+    public static bool Apply(School school, double gameMinutes)
+    {
+        if (gameMinutes <= 0 || school.Roster is null)
+        {
+            return false;
+        }
+
+        var dayNumber = DateOnly.FromDateTime(school.Clock.Time).DayNumber;
+        var changed = false;
+        foreach (var person in school.Roster.People)
+        {
+            changed |= HealthConditions.Tick(person, school.PeopleSeed, dayNumber, gameMinutes);
+        }
+
+        return changed;
+    }
+}