fix: correct Material UI icon naming in Header.tsx and update timetable components

- Fix icon naming: remove 'Icon' suffix from MUI icon components in Header.tsx
  (AccessTime, Close, Person, School, Schedule, Class, Book, Settings, Student, Login, Logout)
- Update timetable components to use UserContext instead of ProfileContext
- Fix timetableService naming collision and circular reference
- Update various components for consistency

src/services/timetableService.ts

@@ -325,9 +325,8 @@ export const enrollmentService = {
 // Combined Export
 // ============================================================================
 
-export const timetableService = {
+export const timetableServiceExports = {
   ...classService,
-  ...timetableService,
   ...lessonService,
   ...enrollmentService,
 };