feat: import leftover student fields into notes and show them on the roster

Store leftover CSV columns on hidden student notes, move catalog import to /events/import, and persist Students index columns from Chapter Settings.

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

Tests/Parsers/StudentImportCsvTemplate_Tests.cs

@@ -0,0 +1,30 @@
+using Core.Parsers;
+
+namespace Tests.Parsers;
+
+[TestFixture]
+public class StudentImportCsvTemplate_Tests
+{
+    [Test]
+    public void Build_IncludesRosterAndDefaultLeftoverColumns()
+    {
+        var csv = StudentImportCsvTemplate.Build();
+        var header = csv.Split('\n')[0].TrimEnd('\r');
+
+        Assert.That(header, Does.StartWith("Student Name,Grade,TSA year,State ID,Regional ID,National ID"));
+        Assert.That(header, Does.Contain("Interview Time"));
+        Assert.That(header, Does.Contain("Application"));
+        Assert.That(csv, Does.Contain("\"Last, First\""));
+    }
+
+    [Test]
+    public void Build_UsesConfiguredLeftoverFields_AndSkipsReserved()
+    {
+        var csv = StudentImportCsvTemplate.Build(["Teacher Rec 1", "Grade", "  Application  "]);
+        var header = csv.Split('\n')[0].TrimEnd('\r');
+
+        Assert.That(header, Does.Contain("Teacher Rec 1"));
+        Assert.That(header, Does.Contain("Application"));
+        Assert.That(header.Split(',').Count(c => c.Equals("Grade", StringComparison.OrdinalIgnoreCase)), Is.EqualTo(1));
+    }
+}