feat: Enhance session handling in timetable and UI

- Introduced session types (exams, credits, consultations, coursework defenses) with distinct icons and colors for better visibility in the UI.
- Updated PlansScreen, ScheduleScreen, and WeekGrid to display session information appropriately.
- Modified CalendarView and PlansView to include session indicators in the calendar and plans.
- Enhanced LessonCard and CompactLesson to show session details and adjust styling based on session presence.
- Added new SessionMark component for consistent session representation across Android and iOS.
- Updated server logic to handle session entries from external documents, ensuring accurate timetable representation.
- Improved date parsing to accommodate session-related dates in various formats.
- Added tests to verify session handling and date parsing functionality.

ios/PSUSchedule/Views/HomeView.swift

@@ -305,6 +305,7 @@ private struct FeaturedLesson: View {
         HStack(alignment: .top, spacing: 14) {
             SubjectDot(subject: lesson.subject, size: 14).padding(.top, 6)
             VStack(alignment: .leading, spacing: 6) {
+                if let session = lesson.session { SessionBadge(kind: session) }
                 Text(lesson.subject).font(.title3.bold()).lineLimit(3).foregroundStyle(.primary)
                 HStack(spacing: 10) {
                     Text(slot.timeLabel).font(.body.monospacedDigit()).foregroundStyle(.secondary)