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/stores/timetableStore.ts

@@ -2,6 +2,7 @@ import { create } from 'zustand';
 import { devtools, persist } from 'zustand/middleware';
 import {
   Class,
+  ClassWithRole,
   ClassWithRelations,
   Timetable,
   TimetableWithRelations,
@@ -21,7 +22,7 @@ interface TimetableState {
   // Classes
   classes: Class[];
   currentClass: ClassWithRelations | null;
-  myClasses: Class[];
+  myClasses: ClassWithRole[];
   myTeachingClasses: Class[];
   classesLoading: boolean;
   classesError: string | null;