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/Core/Settings.swift

@@ -109,7 +109,7 @@ final class Settings: @unchecked Sendable {
         "servers", "plexUrl", "plexToken", "plexUser", "plexMachineId", "musicSection", "musicSectionTitle",
         "stemUrl", "stemToken", "plexAccountToken", "stemRoots", "theme", "accent", "albumColorNowPlaying", "highRefreshRate",
         "stemQuality", "cacheLimitGb", "downloadsWifiOnly", "downloadSort", "keepStemMix", "masterVolume", "tabLayout",
-        "karaokeVocals", "karaokeSoftDb", "playbackSpeed", "stemsOnly", "noStems", "precacheCount", "hiddenNowPlaying", "presets", "presetOrder", "hiddenPresets", "lockedPreset", "webStations", "lockScreenMix", "acapella", "crossfadeSec", "sweetFades",
+        "karaokeVocals", "karaokeSoftDb", "playbackSpeed", "stemsOnly", "noStems", "precacheCount", "hiddenNowPlaying", "presets", "presetOrder", "hiddenPresets", "lockedPreset", "webStations", "lockScreenMix", "swipeUpQueue", "acapella", "crossfadeSec", "sweetFades",
     ]
 
     private func read<T>(_ kp: KeyPath<Settings, T>, _ key: String, _ def: T) -> T {
@@ -216,6 +216,8 @@ final class Settings: @unchecked Sendable {
     var accent: Accent { get { readEnum(\.accent, "accent", .Music) } set { writeEnum(\.accent, "accent", newValue, .Music) } }
     /// Spells the A Cappella mix "Acapella". MixPresets reads the key directly.
     var acapella: Bool { get { read(\.acapella, "acapella", false) } set { write(\.acapella, "acapella", newValue, false) } }
+    /// Swipe up on Now Playing opens Playing Next.
+    var swipeUpQueue: Bool { get { read(\.swipeUpQueue, "swipeUpQueue", true) } set { write(\.swipeUpQueue, "swipeUpQueue", newValue, true) } }
     var lockScreenMix: Bool { get { read(\.lockScreenMix, "lockScreenMix", false) } set { write(\.lockScreenMix, "lockScreenMix", newValue, false) } }
     var albumColorNowPlaying: Bool { get { read(\.albumColorNowPlaying, "albumColorNowPlaying", false) } set { write(\.albumColorNowPlaying, "albumColorNowPlaying", newValue, false) } }
     var highRefreshRate: Bool { get { read(\.highRefreshRate, "highRefreshRate", true) } set { write(\.highRefreshRate, "highRefreshRate", newValue, true) } }