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/Views/Notifications/NotificationsView.swift

@@ -104,7 +104,7 @@ struct NotificationRowView: View {
                 Text(notification.subject)
                     .font(.body)
                     .fontWeight(notification.isRead ? .regular : .semibold)
-                Text(notification.createdAt.relativeFormatted)
+                Text(notification.createdAt, style: .relative)
                     .font(.caption)
                     .foregroundStyle(.secondary)
             }
@@ -114,15 +114,3 @@ struct NotificationRowView: View {
         .padding(.vertical, 4)
     }
 }
-
-extension Date {
-    var relativeFormatted: String {
-        Date.relativeDateTimeFormatter.localizedString(for: self, relativeTo: Date())
-    }
-
-    private static let relativeDateTimeFormatter: RelativeDateTimeFormatter = {
-        let formatter = RelativeDateTimeFormatter()
-        formatter.locale = Locale(identifier: "ru_RU")
-        return formatter
-    }()
-}