Enhance event occurrence parsing with school level filtering

This commit introduces a new SchoolLevel enum and updates the EventOccurrenceParser to filter event occurrences based on the specified school level (Middle School or High School). The EventOccurrenceParseResult and EventOccurrenceParserResult classes have been updated to track skipped section headers and counts for both school levels. Additionally, the EventOccurrenceParserService has been modified to read the school level from configuration, and the UI has been updated to allow users to select the school level for event imports. This enhancement improves the accuracy of event parsing and provides better user feedback on skipped occurrences.

WebApp/Models/ChapterSettings.cs

@@ -1,3 +1,5 @@
+using Core.Models;
+
 namespace WebApp.Models;
 
 /// <summary>
@@ -34,4 +36,9 @@ public class ChapterSettings
     /// Competition year (e.g., "2026")
     /// </summary>
     public string CompetitionYear { get; set; } = "2026";
+
+    /// <summary>
+    /// School level for the chapter (null = import both MS and HS events)
+    /// </summary>
+    public SchoolLevel? SchoolLevel { get; set; }
 }