Implement interval intersection and subtraction methods in GridCoverage, update GridPlan and related DTOs for PlanNote integration

Added new methods for intersecting and subtracting time intervals in the GridCoverage class to enhance scheduling capabilities. Updated the GridPlan and GridPlanDto classes to replace string notes with a structured PlanNote type, improving note management. Enhanced the GridPlanner class to utilize these new features, ensuring better handling of scheduling conflicts and notes during grid generation. Adjusted related tests to validate the new functionality.

backend/tests/TeleWave.Application.Tests/Programming/GridPlanPreviewTests.cs

@@ -78,7 +78,7 @@ public class GridPlanPreviewTests
                 Slot("Повтор", SlotKind.Repeat, SlotBlockMode.FillSlot, 1),
                 Slot("Конец вещания", SlotKind.SignOff, SlotBlockMode.FillSlot, 1),
             ],
-            ["замечание"],
+            [new PlanNote(false, "замечание")],
             SlotsToRemove: 4,
             FallbackGroupId: Guid.NewGuid(),
             FallbackGroupName: "Фон",
@@ -92,7 +92,7 @@ public class GridPlanPreviewTests
         Assert.Equal(plan.Profile.Name, dto.ProfileName);
         Assert.Equal(4, dto.SlotsToRemove);
         Assert.Equal("Фон", dto.FallbackGroupName);
-        Assert.Equal(["замечание"], dto.Notes);
+        Assert.Equal(["замечание"], dto.Notes.Select(n => n.Text));
 
         // Описание блока — то, что читает админ вместо режима и числа.
         Assert.Equal(