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/PlaybackManager.swift

@@ -592,9 +592,22 @@ final class PlaybackManager: StemEngineListener, @unchecked Sendable {
     func saveSongMix() { setSongMix(MixPresets.normalized(mix)) }
     func forgetSongMix() { setSongMix(nil) }
 
+    /// From a backup: its saved mixes replace this phone's for the same songs.
+    func importSongMixes(_ m: [String: [String: StemSetting]]) {
+        guard !m.isEmpty else { return }
+        songMixes.merge(m) { _, new in new }
+        saveSongMixes()
+        // The playing song picks up its restored mix right away.
+        if let s = songMix { applyMix(s) }
+    }
+
     private func setSongMix(_ m: [String: StemSetting]?) {
         guard let key = current?.track.ratingKey else { return }
         songMixes[key] = m
+        saveSongMixes()
+    }
+
+    private func saveSongMixes() {
         let all = songMixes, file = songMixFile
         DispatchQueue.global(qos: .utility).async {
             if let data = try? JSONEncoder().encode(all) { try? data.write(to: file, options: .atomic) }

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) {