Enhance school day structure and decision-making for lunch breaks

- Updated `ai.md` to clarify the mechanics of hunger restoration and the importance of lunch breaks in the school schedule.
- Revised `schedule.md` to detail the new lunch break structure, allowing for separate sittings for different grade levels.
- Enhanced `Decision.cs` and `DecisionPlanner.cs` to incorporate logic for lunch breaks, ensuring that students only leave lessons during their designated lunch windows.
- Updated `DayFrameDef` and related classes to support multiple lunch breaks and validate their configurations.
- Adjusted tests to validate the new decision-making logic regarding lunch breaks and hunger management, ensuring robust functionality.
- Improved localization strings to reflect changes in the school day structure and lunch functionalities.

src/HSchool.Simulation/SchoolCreationError.cs

@@ -0,0 +1,18 @@
+namespace HSchool.Simulation;
+
+/// <summary>
+/// Why a school could not be created. Lives here rather than in the server because the checks
+/// that produce it — the name rules, the clock range — belong to the simulation.
+/// </summary>
+public enum SchoolCreationError
+{
+    None = 0,
+    LimitReached,
+    InvalidName,
+    InvalidStartDate,
+    InvalidMap,
+    UnknownMod,
+    InvalidCatalog,
+    UnknownNameSet,
+    UnknownNativeLanguage,
+}