iOS: Duo layout fixes, swipe-up option, fuller backup restore

- DuoRail sits at the bottom of the strip, clear of the back buttons
- Setting to turn off swipe up for Playing Next
- Tighter Now Playing on iPhone Duo (folded and docked), regular phones unchanged
- Bigger stacked stem faders in the Duo deck
- Backup v2 restores song mixes, custom presets and stem playlist covers

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ios/Stemify/UI/RootView.swift

@@ -238,16 +238,18 @@ private struct DuoRail: View {
     @Environment(\.palette) private var p
 
     var body: some View {
+        // Sits at the bottom of the strip: the top is where the panes' back buttons and the
+        // status bar live, and the tabs used to land right on them.
         VStack(spacing: 4) {
-            Spacer(minLength: 48)
+            Spacer(minLength: 160)
             item("Playing", "waveform", on: ui.deck) { ui.showDeck() }
             ForEach(ui.tabs, id: \.self) { t in
                 item(t.rawValue, t.icon, on: !ui.deck && ui.tab == t) { ui.selectTab(t) }
             }
             Capsule().fill(p.label3.opacity(0.4)).frame(width: 24, height: 2).padding(.vertical, 8)
             item("Swap", "arrow.left.arrow.right", on: false) { swap.toggle() }
-            Spacer(minLength: 48)
         }
+        .padding(.bottom, 20)
         .frame(maxWidth: .infinity)
     }