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/FuzzyStudentMatcher_Tests.cs

@@ -0,0 +1,41 @@
+using Core.Parsers;
+using Tests.Builders;
+
+namespace Tests.Parsers;
+
+[TestFixture]
+public class FuzzyStudentMatcher_Tests
+{
+    [SetUp]
+    public void SetUp() => StudentBuilder.ResetIdCounter();
+
+    [Test]
+    public void Find_MatchesNicknameAmongTwoJosiahs()
+    {
+        var jo = StudentBuilder.Create("Josiah", "Brown").WithNickname("Jo").Build();
+        var josiahB = StudentBuilder.Create("Josiah", "Green").WithNickname("Josiah B").Build();
+
+        var match = FuzzyStudentMatcher.Find([jo, josiahB], "Jo");
+
+        Assert.That(match, Is.Not.Null);
+        Assert.That(match!.Value.Student.Id, Is.EqualTo(jo.Id));
+    }
+
+    [Test]
+    public void Score_LegalNameStillMatchesWhenNicknameSet()
+    {
+        var jo = StudentBuilder.Create("Josiah", "Brown").WithNickname("Jo").Build();
+
+        Assert.That(FuzzyStudentMatcher.Score(jo, "Josiah Brown"), Is.GreaterThanOrEqualTo(FuzzyStudentMatcher.MatchThreshold));
+        Assert.That(FuzzyStudentMatcher.Score(jo, "Brown, Josiah"), Is.GreaterThanOrEqualTo(FuzzyStudentMatcher.MatchThreshold));
+    }
+
+    [Test]
+    public void Score_NullNicknameDoesNotThrow()
+    {
+        var student = StudentBuilder.Create("Aria", "Cole").Build();
+
+        Assert.That(FuzzyStudentMatcher.Score(student, "Aria Cole"), Is.GreaterThanOrEqualTo(FuzzyStudentMatcher.MatchThreshold));
+        Assert.That(FuzzyStudentMatcher.Find([student], "Nobody"), Is.Null);
+    }
+}