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/pages/timetable/MyClassesPage.tsx

@@ -8,8 +8,8 @@ const MyClassesPage: React.FC = () => {
   const { profile } = useUser();
   const {
     myClasses,
-    myClassesLoading,
-    myClassesError,
+    classesLoading: myClassesLoading,
+    classesError: myClassesError,
     fetchMyClasses,
   } = useTimetableStore();