Support iOS 26 soft scroll edge effects in CalendarViewRepresentable

[ikeval]

Description

CalendarViewRepresentable does not reliably support the iOS 26 soft scroll-edge effect when embedded in a SwiftUI NavigationStack.

Applying .scrollEdgeEffectStyle(.soft, for: .top) to the representable still produces a hard navigation-bar edge. After scrolling far enough through past months, the navigation-bar background can disappear completely. The title and toolbar items remain visible, but calendar content is then shown directly behind them.

This reproduces in a minimal view without custom calendar item views or overlays.

Reproduction

import HorizonCalendar
import SwiftUI

struct CalendarTestView: View {
    @StateObject private var calendarProxy = CalendarViewProxy()

    var body: some View {
        NavigationStack {
            CalendarViewRepresentable(
                visibleDateRange: Date.distantPast...Date.now,
                monthsLayout: .vertical,
                dataDependency: nil,
                proxy: calendarProxy
            )
            .scrollEdgeEffectStyle(.soft, for: .top)
            .onAppear {
                calendarProxy.scrollToDay(
                    containing: .now,
                    scrollPosition: .centered,
                    animated: false
                )
            }
            .ignoresSafeArea()
            .navigationTitle("Calendar Test")
            .toolbar {
                ToolbarItem(placement: .primaryAction) {
                    Button("Add", systemImage: "plus") { }
                }
            }
        }
    }
}

1. Present CalendarTestView.
2. Scroll backward through past months.
3. Observe the top navigation-bar edge and background.

Expected behavior

The soft top scroll-edge effect remains visible and stable while the calendar scrolls.

Actual behavior

The top edge remains hard, and the navigation-bar background can disappear entirely after scrolling through past months.

Environment

• Xcode 26.6 (17F113)
• iOS 26 Simulator
• HorizonCalendar master revision 363088cc5d6930eb464d582493632882be6766fe

Additional context

CalendarViewRepresentable wraps CalendarView, whose internal scrolling view is a private CalendarScrollView. The SwiftUI modifier appears unable to configure that inner scroll view. It may help to apply topEdgeEffect.style = .soft internally on iOS 26 or expose a public configuration hook for the calendar scroll view.