Teacher lookup flow:
1. Get user by auth → retrieve email
2. Query timetable_entries by teacher_email → get schedule

// lib/api/timetable.ts

// Get schedule by email (primary method)
getTeacherScheduleByEmail(email: string, academicYear?: string): Promise<WeeklyTimetable>

// Get current user's schedule
getCurrentUserSchedule(userId: string, academicYear?: string): Promise<{
  weekly: WeeklyTimetable;
  stats: TeacherScheduleStats;
  periods: TimetablePeriod[];
}>

// Utilities
getCurrentDayOfWeek(): DayOfWeek | null  // null on weekends
formatPeriodTime(period: TimetablePeriod): string

const handleCellClick = (entry: TimetableEntryWithPeriod) => {
  if (!entry.course_id) return;

  if (entry.course_type === "ev" || entry.course_type === "kcfs") {
    // EV/KCFS: Navigate to course page
    window.location.href = `/class/${entry.course_id}`;
  } else {
    // English: Navigate to attendance page
    window.location.href = `/class/${entry.course_id}/attendance`;
  }
};