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.

frontend/src/shared/api/types.ts

@@ -726,11 +726,14 @@ export type GridPlanSlotDto = {
   block: string
 }
 
+/** Замечание к плану: `isError` — то, что после сборки останется дырой в эфире. */
+export type PlanNoteDto = { isError: boolean; text: string }
+
 export type GridPlanDto = {
   profile: GridProfileKind
   profileName: string
   slots: GridPlanSlotDto[]
-  notes: string[]
+  notes: PlanNoteDto[]
   /** Больше нуля только при пересборке — столько слотов будет снесено. */
   slotsToRemove: number
   fallbackGroupName: string | null