feat: deliver Riverside Schedule seven-day grid and school HTML import

mobile/lib/data/json_schedule_import.dart

@@ -8,11 +8,13 @@ class ImportDraft {
     required this.explicitlyEmpty,
     required this.source,
     required this.parserVersion,
+    this.semesterLabel,
   });
   final List<Course> courses;
   final bool explicitlyEmpty;
   final CourseSource source;
   final String parserVersion;
+  final String? semesterLabel;
 }
 
 class JsonScheduleImport {

mobile/lib/data/schedule_file_import.dart

@@ -0,0 +1,17 @@
+import 'json_schedule_import.dart';
+import '../domain/course.dart';
+import '../features/school/school_page_adapter.dart';
+
+class ScheduleFileImport {
+  static ImportDraft parse(String content) {
+    final trimmed = content.replaceFirst('\uFEFF', '').trimLeft();
+    if (trimmed.startsWith('<')) {
+      return SchoolPageAdapter().extract(
+        trimmed,
+        Uri.parse('https://yjsjy.uestc.edu.cn/pyxx/pygl/xskbcx/index/1'),
+        source: CourseSource.file,
+      );
+    }
+    return JsonScheduleImport.parse(trimmed);
+  }
+}