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;
+    }
+}

src/HSchool.Simulation/School.cs

@@ -348,7 +348,7 @@ public sealed class School : IDisposable
         }
     }
 
-    /// <summary>Runs one fixed step of the school: calendar, yearly intake, applicant refresh, presence, actions, need decay, then apparel wear.</summary>
+    /// <summary>Runs one fixed step of the school: calendar, yearly intake, applicant refresh, presence, actions, need decay, apparel wear, then health conditions.</summary>
     /// <returns><see langword="true"/> when the roster, applicant pool or wardrobe changed this step.</returns>
     public bool Tick(double deltaTime, double gameMinutesPerRealSecond)
     {
@@ -442,6 +442,7 @@ public sealed class School : IDisposable
             peopleChanged |= AffinitySystem.Apply(this, talked);
         }
 
+        peopleChanged |= HealthConditionSystem.Apply(this, gameMinutes);
         peopleChanged |= RosterTalkDirty;
         RosterTalkDirty = false;
         return peopleChanged;