Add EventDef notices, morning and lesson bells, and info toasts.

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

src/HSchool.Simulation/EventSystem.cs

@@ -0,0 +1,48 @@
+using HSchool.Content;
+
+namespace HSchool.Simulation;
+
+/// <summary>
+/// Turns clock edges into world facts. One dayStart per morning crossing, one lessonStart per
+/// school when the bell enters a lesson period — not one per class.
+/// </summary>
+internal static class EventSystem
+{
+    public static IReadOnlyList<WorldEvent> Detect(School school, DateTime before, DateTime after)
+    {
+        if (school.Catalog is null || after <= before)
+        {
+            return [];
+        }
+
+        var facts = new List<WorldEvent>(2);
+        if (CrossedWorkMorning(school.Catalog, before, after, school.SchoolWeekDays))
+        {
+            facts.Add(new WorldEvent(EventTriggers.DayStart));
+        }
+
+        if (EnteredLessonPeriod(school.Catalog, before, after, school.SchoolWeekDays))
+        {
+            facts.Add(new WorldEvent(EventTriggers.LessonStart));
+        }
+
+        return facts;
+    }
+
+    private static bool CrossedWorkMorning(DefCatalog catalog, DateTime before, DateTime after, int weekDays)
+    {
+        if (!PersonDayLog.CrossedDayStart(before, after))
+        {
+            return false;
+        }
+
+        return SchoolDay.IsWorkday(catalog, after, weekDays);
+    }
+
+    private static bool EnteredLessonPeriod(DefCatalog catalog, DateTime before, DateTime after, int weekDays)
+    {
+        var beforeSlot = SchoolDay.At(catalog, before, weekDays);
+        var afterSlot = SchoolDay.At(catalog, after, weekDays);
+        return afterSlot.Kind == DaySlotKind.Lesson && beforeSlot != afterSlot;
+    }
+}