Refactor collection initializers to use C# 12 collection expressions

This commit updates various files across the Core and WebApp projects to replace traditional collection initializers with C# 12 collection expressions. Changes include modifications to EventAssignment.cs, TeamScheduler_DecisionTree.cs, CareerField.cs, EventDefinition.cs, and several components in the WebApp. These updates enhance code readability and maintainability by adhering to modern C# syntax standards.

Core/Entities/CareerField.cs

@@ -43,13 +43,10 @@ public class CareerField
 		Id = id;
 		Name = name;
 		Description = description;
-		DirectCareerMatches = directCareerMatches ?? Array.Empty<string>();
-		PatternKeywords = patternKeywords ?? Array.Empty<string>();
+		DirectCareerMatches = directCareerMatches ?? [];
+		PatternKeywords = patternKeywords ?? [];
 	}
 
-	public override string ToString()
-	{
-		return Name;
-	}
+	public override string ToString() => Name;
 }