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>

Core/Models/StudentNotesImportResult.cs

@@ -0,0 +1,48 @@
+using Core.Entities;
+using Core.Notes;
+
+namespace Core.Models;
+
+/// <summary>
+/// Result of parsing a student notes field CSV.
+/// </summary>
+public class StudentNotesImportResult
+{
+    public List<StudentNotesImportMatch> Matches { get; set; } = [];
+
+    public List<StudentNotesImportIssue> Issues { get; set; } = [];
+
+    public List<string> Errors { get; set; } = [];
+
+    public List<string> Warnings { get; set; } = [];
+
+    public IReadOnlyList<string> FieldNames { get; set; } = [];
+
+    public bool IsSuccess => Errors.Count == 0;
+
+    public int StudentsWithChanges => Matches.Count(m => m.Merge.Changed);
+}
+
+public class StudentNotesImportMatch
+{
+    public required Student Student { get; set; }
+
+    public string RawStudentName { get; set; } = string.Empty;
+
+    public int RowNumber { get; set; }
+
+    public int StudentScore { get; set; }
+
+    public List<ImportedField> IncomingFields { get; set; } = [];
+
+    public required ImportedFieldsMergeResult Merge { get; set; }
+}
+
+public class StudentNotesImportIssue
+{
+    public int RowNumber { get; set; }
+
+    public string RawStudentName { get; set; } = string.Empty;
+
+    public string Message { get; set; } = string.Empty;
+}