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.Content/Defs.cs

@@ -54,6 +54,13 @@ public sealed class ActionDef : Def
 
     /// <summary>Leisure weight. Zero means phase 21 will not pick this for fun — only for a need.</summary>
     public float Weight { get; init; }
+
+    /// <summary>
+    /// A sitting rather than something done whenever the need bites: only offered during the
+    /// eater's own lunch break (<see cref="DayFrameDef.LunchBreaks"/>). Without it a hungry class
+    /// would walk out of a lesson to the canteen, and the whole school would arrive at once.
+    /// </summary>
+    public bool Lunch { get; init; }
 }
 
 public sealed class ThingDef : Def