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/SessionMark.swift

@@ -0,0 +1,90 @@
+import SwiftUI
+import UIKit
+
+/// The session's events: exams, credits, consultations and coursework defences. They wear an
+/// amber of their own — red would read as an error — and each kind its own symbol, so they
+/// stand out from ordinary lessons in the schedule, the calendar and the plans.
+enum SessionKind {
+    case exam, credit, defence, consultation
+
+    init?(_ type: String) {
+        switch type {
+        case "Экзамен": self = .exam
+        case "Зачёт": self = .credit
+        case "Защита курсовой работы": self = .defence
+        case "Консультация": self = .consultation
+        default: return nil
+        }
+    }
+
+    var label: String {
+        switch self {
+        case .exam: "Экзамен"
+        case .credit: "Зачёт"
+        case .defence: "Защита курсовой"
+        case .consultation: "Консультация"
+        }
+    }
+
+    var symbol: String {
+        switch self {
+        case .exam: "pencil.and.list.clipboard"
+        case .credit: "checkmark.seal.fill"
+        case .defence: "graduationcap.fill"
+        case .consultation: "bubble.left.and.bubble.right.fill"
+        }
+    }
+
+    /// Exams, credits and defences are filled; consultations are tonal.
+    var strong: Bool { self != .consultation }
+
+    var fill: Color { strong ? .sessionStrong : .sessionSoft }
+    var content: Color { strong ? .onSessionStrong : .onSessionSoft }
+}
+
+extension Lesson {
+    var session: SessionKind? { SessionKind(type) }
+}
+
+private func dynamic(_ light: UInt32, _ dark: UInt32) -> Color {
+    func ui(_ hex: UInt32) -> UIColor {
+        UIColor(red: CGFloat((hex >> 16) & 0xFF) / 255, green: CGFloat((hex >> 8) & 0xFF) / 255, blue: CGFloat(hex & 0xFF) / 255, alpha: 1)
+    }
+    return Color(UIColor { $0.userInterfaceStyle == .dark ? ui(dark) : ui(light) })
+}
+
+extension Color {
+    /// The session amber (an M3 tonal palette from #8A5100): text, marks and outlines.
+    static let sessionAccent = dynamic(0x8A5100, 0xFFB95C)
+    static let sessionStrong = dynamic(0x8A5100, 0xFFB95C)
+    static let onSessionStrong = dynamic(0xFFFFFF, 0x482900)
+    static let sessionSoft = dynamic(0xFFDDB8, 0x693C00)
+    static let onSessionSoft = dynamic(0x2C1600, 0xFFDDB8)
+}
+
+/// "Зачёт" with its symbol, as a capsule above the subject.
+struct SessionBadge: View {
+    var kind: SessionKind
+    var body: some View {
+        Label(kind.label, systemImage: kind.symbol)
+            .font(.footnote.weight(.semibold))
+            .padding(.horizontal, 10)
+            .padding(.vertical, 4)
+            .foregroundStyle(kind.content)
+            .background(kind.fill, in: .capsule)
+    }
+}
+
+/// A round marker with the kind's symbol, in place of a subject's dot.
+struct SessionDot: View {
+    var kind: SessionKind
+    var size: CGFloat = 20
+    var body: some View {
+        Image(systemName: kind.symbol)
+            .font(.system(size: size * 0.5, weight: .bold))
+            .foregroundStyle(kind.content)
+            .frame(width: size, height: size)
+            .background(kind.fill, in: .circle)
+            .accessibilityHidden(true)
+    }
+}