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.Server/mods/core/defs/dayframe/standard.jsonc

@@ -6,4 +6,11 @@
   "breakMinutes": 10,
   "longBreakAfter": 3,
   "longBreakMinutes": 20,
+  // Two sittings so the canteen is not the whole school at once: juniors eat after the
+  // third lesson, seniors after the fourth. Both breaks are long because somebody eats in
+  // them. A pack that wants one sitting just drops this list.
+  "lunchBreaks": [
+    { "afterLesson": 3, "gradeMin": 1, "gradeMax": 5 },
+    { "afterLesson": 4, "gradeMin": 6, "gradeMax": 11 },
+  ],
 }