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>

WebApp/Services/INotesService.cs

@@ -22,6 +22,26 @@ public interface INotesService
     /// <returns>The note with title "#{pageIdentifier}" or null if not found</returns>
     Task<Note?> GetPageNoteAsync(string pageIdentifier);
 
+    /// <summary>
+    /// Gets the system note for a student, or null if none exists.
+    /// </summary>
+    Task<Note?> GetStudentNoteAsync(int studentId);
+
+    /// <summary>
+    /// Gets system notes for the given student ids, keyed by student id.
+    /// </summary>
+    Task<IReadOnlyDictionary<int, Note>> GetStudentNotesAsync(IEnumerable<int> studentIds);
+
+    /// <summary>
+    /// Soft-deletes system notes for the given student ids.
+    /// </summary>
+    Task SoftDeleteStudentNotesAsync(IEnumerable<int> studentIds, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Distinct Field names from student note <c>## Imported fields</c> tables.
+    /// </summary>
+    Task<IReadOnlyList<string>> GetImportedFieldNamesAsync(CancellationToken cancellationToken = default);
+
     /// <summary>
     /// Gets all history entries for a note.
     /// </summary>