fix: address all PR review comments

- HTTPClient: replace isRefreshing bool with shared Task to safely
  coalesce concurrent 401 refresh attempts; surface JSON serialization
  error instead of silently dropping request body
- AuthService.logout: always clear Keychain tokens via defer, even when
  refresh token is absent, preventing stale access token
- NotificationsAPIService: remove updateAppBadge (UIKit call moved to
  @MainActor NotificationsViewModel); drop unused UIKit import
- NotificationsViewModel: guard startPolling() against duplicate tasks;
  update badge directly on @MainActor instead of hopping to actor
- VerifyEmailView: replace Timer (never invalidated) with async Task
  cancelled in .onDisappear
- NotificationsView: use Text(date, style: .relative) — auto-updates
  without custom formatter; remove duplicate Date extension
- SettingsView: handle logoutAll errors explicitly with alert instead of
  silently proceeding with local logout
- MaydayLiveActivity/Info.plist: add NSExtensionPrincipalClass so the
  widget extension is discoverable by the system
- Live Activity widget: replace frozen duration(from:) with
  Text(date, style: .timer); replace frozen relativeFormatted with
  Text(date, style: .relative); localize status badge to Russian

Co-authored-by: robonen <26167508+robonen@users.noreply.github.com>

Mayday/ViewModels/NotificationsViewModel.swift

@@ -1,5 +1,6 @@
 import Foundation
 import SwiftUI
+import UIKit
 
 @MainActor
 class NotificationsViewModel: ObservableObject {
@@ -70,8 +71,8 @@ class NotificationsViewModel: ObservableObject {
     }
 
     func startPolling() {
-        // Polling always reloads page 1 to pick up new notifications.
-        // Users who have scrolled to older pages will have the list reset on each interval.
+        // Guard against starting a second polling loop if already running.
+        guard pollingTask == nil else { return }
         pollingTask = Task {
             while !Task.isCancelled {
                 try? await Task.sleep(for: .seconds(30))
@@ -88,8 +89,6 @@ class NotificationsViewModel: ObservableObject {
 
     private func updateBadge() {
         let unreadCount = notifications.filter { !$0.isRead }.count
-        Task {
-            await service.updateAppBadge(unreadCount)
-        }
+        UIApplication.shared.applicationIconBadgeNumber = unreadCount
     }
 }