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/StudentNotesFieldParser_Tests.cs

@@ -34,6 +34,22 @@ public class StudentNotesFieldParser_Tests
         Assert.That(result.Issues[0].RawStudentName, Is.EqualTo("Nobody Here"));
     }
 
+    [Test]
+    public void Parse_MatchesNicknamePlusLastName()
+    {
+        var jo = StudentBuilder.Create("Josiah", "Brown").WithNickname("Jo").Build();
+        const string csv = """
+            Student Name,Interview Time
+            Jo Brown,3:20-3:35
+            """;
+
+        var result = Parse(csv, [jo]);
+
+        Assert.That(result.IsSuccess, Is.True);
+        Assert.That(result.Matches, Has.Count.EqualTo(1));
+        Assert.That(result.Matches[0].Student, Is.SameAs(jo));
+    }
+
     [Test]
     public void Parse_SameExistingNote_HasNoChanges()
     {