Animate page indicator button with cascading pull-down hint

TimelineView drives a 2.4s cycle: two sin-bell chevron pulses
(primary + ghost trailing 7pt below) then a pause. Mirrors the
cascadingArrows pattern — suggests pull-down on all three pages.

Co-Authored-By: Kutesir <kutesir@provoc.ug>
Co-Authored-By: Sentry <sentry@provoc.ug>

Features/Backup/BackupView.swift

@@ -941,15 +941,34 @@ struct BackupView: View {
                 }
             }
 
-            // Square advance button with amber border
+            // Square advance button — animated to hint pull-down
             Button {
                 withAnimation(.spring(response: 0.4, dampingFraction: 0.85)) {
                     ringPage = (ringPage + 1) % ringPageCount
                 }
             } label: {
+                TimelineView(.animation(minimumInterval: 1.0 / 30)) { tl in
+                    let t = tl.date.timeIntervalSince1970
+                    // 2.4s cycle: two cascading pulses then a long pause
+                    let cycle = t.truncatingRemainder(dividingBy: 2.4)
+                    let p1 = indicatorChevronPhase(cycle, start: 0.00, duration: 0.38)
+                    let p2 = indicatorChevronPhase(cycle, start: 0.42, duration: 0.38)
+
+                    ZStack {
+                        // Primary chevron
                         Image(systemName: "chevron.down")
                             .font(.system(size: 9, weight: .medium))
                             .foregroundStyle(AppTheme.inkSecondary)
+                            .offset(y: CGFloat(p1) * 4)
+                            .opacity(1.0 - p1 * 0.35)
+                        // Ghost — trails below with delay
+                        Image(systemName: "chevron.down")
+                            .font(.system(size: 8, weight: .medium))
+                            .foregroundStyle(AppTheme.inkSecondary.opacity(0.45))
+                            .offset(y: CGFloat(p2) * 4 + 7)
+                            .opacity(p2 * 0.85)
+                    }
+                }
                 .frame(width: 30, height: 30)
                 .overlay(
                     RoundedRectangle(cornerRadius: 7, style: .continuous)
@@ -961,6 +980,13 @@ struct BackupView: View {
         .frame(maxWidth: .infinity)
     }
 
+    // sin-bell phase: rises from 0→1→0 over `duration` seconds starting at `start`
+    private func indicatorChevronPhase(_ cycle: Double, start: Double, duration: Double) -> Double {
+        let t = cycle - start
+        guard t >= 0, t < duration else { return 0 }
+        return sin(t / duration * .pi)
+    }
+
     // MARK: — Storage helpers
 
     private func storageStat(_ value: String, label: String, color: Color) -> some View {