feat: add CSV import for student event rankings

Let advisors load preference ranks from a converted CSV with fuzzy matching, known aliases, and a parse-preview-save page instead of relying on the ranking editor.

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

Core/Services/IStudentEventRankingImportService.cs

@@ -0,0 +1,15 @@
+using Core.Entities;
+using Core.Models;
+
+namespace Core.Services;
+
+/// <summary>
+/// Parses student event ranking CSV data against existing students and events.
+/// </summary>
+public interface IStudentEventRankingImportService
+{
+    /// <summary>
+    /// Parses ranking CSV from a stream. The stream is not disposed.
+    /// </summary>
+    StudentEventRankingParseResult Parse(Stream stream, ICollection<Student> students, ICollection<EventDefinition> events);
+}