fix(nav): trim burger menu, fix MyClasses for teachers, fix NotFound crash

- Header: trim menu to My Work section (My Lessons, My Classes, Lesson Plans), School Admin (gated), Platform Admin (gated)
- MyClassesPage: fix loading/error state destructure (classesLoading not myClassesLoading)
- NotFound: fix ErrorOutline -> ErrorOutlineIcon to prevent 404 page crash
- timetableService: getMyClasses now calls both /me/teacher and /me/student, merges with role annotation
- timetableStore: myClasses type updated to ClassWithRole[]
- timetable.types: add ClassWithRole interface and code/institute_id optional fields to Class

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

src/types/timetable.types.ts

@@ -27,6 +27,15 @@ export interface Class {
   created_at: string;
   updated_at: string;
   is_active: boolean;
+  code?: string;
+  institute_id?: string;
+}
+
+export interface ClassWithRole extends Class {
+  role: 'teacher' | 'student' | 'assistant';
+  status: string;
+  class_id?: string;
+  is_primary_teacher?: boolean;
 }
 
 export interface ClassTeacher {