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.

tests/HSchool.AppHost.Tests/StaffingApiTests.cs

@@ -179,25 +179,10 @@ public class StaffingApiTests(AppHostFixture fixture)
         Assert.True(assigned.Payroll > hired.Payroll);
         Assert.Equal(2, assigned.Staff.Single().Subjects.Count);
 
-        using var over = await client.PostAsJsonAsync(
-            $"/api/schools/{school.Id}/staff/{Uri.EscapeDataString(teacher.Id)}/subjects",
-            new { subject = "Literature" },
-            TestContext.Current.CancellationToken);
-        // Cheap asks may still fit; only the numbers matter when the cap actually bites.
-        if (over.StatusCode == HttpStatusCode.Conflict)
-        {
-            var problem = await over.Content.ReadFromJsonAsync<ProblemResponse>(TestContext.Current.CancellationToken);
-            Assert.Equal("payroll-exceeded", problem?.Code);
-            Assert.True(problem?.Attempted > problem?.Allocated);
-            Assert.Equal(assigned.Payroll, problem?.Payroll);
-        }
-        else
-        {
-            over.EnsureSuccessStatusCode();
-            assigned = await over.Content.ReadFromJsonAsync<StaffingResponse>(TestContext.Current.CancellationToken);
-            Assert.NotNull(assigned);
-        }
-
+        // A third subject used to be tried here with an if/else around the cap, which meant the
+        // test passed whichever way it went. The refusal has its own test now
+        // (AssigningPastTheCap_IsRejectedWithTheNumbers); this one is about assign, unassign and
+        // what survives a restart.
         var payrollWithSubjects = assigned.Payroll;
         using var unassign = await client.DeleteAsync(
             $"/api/schools/{school.Id}/staff/{Uri.EscapeDataString(teacher.Id)}/subjects/RussianLanguage",