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/Parsers/StudentImportCsvTemplate.cs

@@ -0,0 +1,63 @@
+using Core.Notes;
+
+namespace Core.Parsers;
+
+/// <summary>
+/// Builds a starter CSV for <c>/students/import</c> with roster columns plus leftover note fields.
+/// </summary>
+public static class StudentImportCsvTemplate
+{
+    public static readonly string[] RosterHeaders =
+    [
+        "Student Name",
+        "Grade",
+        "TSA year",
+        "State ID",
+        "Regional ID",
+        "National ID"
+    ];
+
+    /// <summary>
+    /// Returns a CSV with a header row and one example data row.
+    /// </summary>
+    public static string Build(IEnumerable<string>? leftoverFieldNames = null)
+    {
+        List<string> leftovers = leftoverFieldNames?
+            .Where(name => !string.IsNullOrWhiteSpace(name))
+            .Select(name => name.Trim())
+            .Where(name => !StudentNotesFieldParser.IsReservedHeader(name))
+            .Distinct(StringComparer.OrdinalIgnoreCase)
+            .ToList() ?? [];
+
+        if (leftovers.Count == 0)
+            leftovers = [.. StudentNoteFieldDefaults.IndexColumns];
+
+        var headers = RosterHeaders.Concat(leftovers).ToArray();
+        var values = headers.Select(ExampleValue).ToArray();
+        return $"{ToCsvRow(headers)}{Environment.NewLine}{ToCsvRow(values)}{Environment.NewLine}";
+    }
+
+    private static string ExampleValue(string header) => header switch
+    {
+        "Student Name" => "Last, First",
+        "Grade" => "9",
+        "TSA year" => "1st",
+        "Interview Time" => "3:20-3:35",
+        _ when ContainsIgnoreCase(header, "Application")
+               || ContainsIgnoreCase(header, "Permission") => "x",
+        _ => string.Empty
+    };
+
+    private static bool ContainsIgnoreCase(string value, string part) =>
+        value.Contains(part, StringComparison.OrdinalIgnoreCase);
+
+    private static string ToCsvRow(IEnumerable<string> cells) =>
+        string.Join(",", cells.Select(EscapeCsv));
+
+    private static string EscapeCsv(string value)
+    {
+        if (value.Contains(',') || value.Contains('"') || value.Contains('\n'))
+            return $"\"{value.Replace("\"", "\"\"")}\"";
+        return value;
+    }
+}