feat: stundenplan page with timetable, exams, and quicklinks

- Static timetable for all 5 classes (Info1/2, Freko1/2, MR)
- Click-to-highlight subject across week grid
- Cell tooltip with full subject, teacher, room, time
- Today list with remaining lesson count and Freistunde gaps
- Klausurenplan with Bayern Ferien dividers
- iCal export button for weekly schedule
- Quicklinks panel (Notenportal)

index.js

@@ -50,6 +50,7 @@ app.get('/admin', html('admin.html'));
 app.get('/datenschutz', html('datenschutz.html'));
 app.get('/app', html('app.html'));
 app.get('/reset-password', html('reset-password.html'));
+app.get('/stundenplan', html('stundenplan.html'));
 app.get('/{*path}', html('index.html'));
 
 app.listen(PORT, '127.0.0.1', () => {