feat: implement meal planning feature with CRUD operations and UI integration

backend/src/meal-plan/dto/create-meal-plan-entry.dto.ts

@@ -0,0 +1,10 @@
+import { IsDateString, IsInt, IsPositive } from 'class-validator';
+
+export class CreateMealPlanEntryDto {
+  @IsDateString()
+  date: string; // YYYY-MM-DD
+
+  @IsInt()
+  @IsPositive()
+  recipeId: number;
+}