feat: add optional student nickname for informal display

Keep legal first and last names for formal lists; show DisplayFirstName on teams, calendars, and import matching so two Josiahs can be told apart.

Co-authored-by: Cursor <cursoragent@cursor.com>

Tests/Parsers/TeamParser_Tests.cs

@@ -1,3 +1,7 @@
+using System.Text;
+using Core.Parsers;
+using Tests.Builders;
+
 namespace Tests.Parsers;
 
 public class TeamParser_Tests
@@ -37,4 +41,26 @@ public class TeamParser_Tests
 		}
 	}
 
+	[Test]
+	public void Parse_MatchesNicknameAndLegalStudentColumns()
+	{
+		StudentBuilder.ResetIdCounter();
+		var jo = StudentBuilder.Create("Josiah", "Brown").WithNickname("Jo").Build();
+		var josiahB = StudentBuilder.Create("Josiah", "Green").WithNickname("Josiah B").Build();
+		var coding = EventDefinitionBuilder.Team("Coding", 2, 2).Build();
+
+		const string csv = """
+			Team Name,Event Name,Regional Time Slot,Student 1,Student 2
+			A,Coding,,Jo,Josiah Green
+			""";
+
+		using var reader = new StreamReader(new MemoryStream(Encoding.UTF8.GetBytes(csv)));
+		using var parser = new TeamParser(reader);
+		var teams = parser.Parse([coding], [jo, josiahB]);
+
+		Assert.That(teams, Has.Length.EqualTo(1));
+		Assert.That(teams[0].Students.Select(s => s.Id), Is.EquivalentTo(new[] { jo.Id, josiahB.Id }));
+		Assert.That(teams[0].Captain!.Id, Is.EqualTo(jo.Id));
+	}
+
 }