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/Playback/StemPlaylists.swift

@@ -163,22 +163,14 @@ final class StemPlaylists {
         return MixPresets.current(allStems, mix)?.label ?? "Custom Mix"
     }
 
-    /// Brings in playlists from an export: new ids are added, ids already here are replaced when the
-    /// import was updated more recently. Returns how many lists were added or replaced.
+    /// Import from a backup: the backup's copy of each list wins, lists only on this phone stay.
     @discardableResult
-    func merge(_ incoming: [StemPlaylist]) -> Int {
-        var n = 0
+    func restore(_ incoming: [StemPlaylist]) -> Int {
         for pl in incoming {
-            if let i = lists.firstIndex(where: { $0.id == pl.id }) {
-                guard pl.updated > lists[i].updated else { continue }
-                lists[i] = pl
-            } else {
-                lists.append(pl)
-            }
-            n += 1
+            if let i = lists.firstIndex(where: { $0.id == pl.id }) { lists[i] = pl } else { lists.append(pl) }
         }
-        if n > 0 { save() }
-        return n
+        if !incoming.isEmpty { save() }
+        return incoming.count
     }
 
     private func edit(_ id: String, _ change: (inout StemPlaylist) -> Void) {