iOS: export/import stem playlists and sound settings

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

ios/Stemify/UI/Screens/SettingsScreens.swift

@@ -1,4 +1,5 @@
 import SwiftUI
+import UniformTypeIdentifiers
 
 /// A Settings.app row that pushes [route]: icon, title, grey value, chevron.
 private struct NavCell: View {
@@ -147,6 +148,11 @@ struct SettingsScreen: View {
                 NavCell(title: "Cache & Downloads", value: gb(g.cache.usage.cachedBytes), icon: "externaldrive.fill", iconBg: 0x8E8E93, route: .Storage)
                 ToggleCell(title: "Download on Wi-Fi Only", icon: "arrow.down.circle.fill", iconBg: 0x30B0C7, isOn: $s.downloadsWifiOnly)
             } header: { Header(text: "Storage") }
+            Section {
+                BackupCells()
+            } header: { Header(text: "Backup") } footer: {
+                Footer(text: "Stem playlists, their mixes and sound settings. Tokens and server addresses are left out. Save to iCloud Drive from the Files sheet.")
+            }
             Section {
                 NavCell(title: "Appearance", value: s.theme.label, icon: "paintbrush.fill", iconBg: 0x007AFF, route: .Appearance)
             } header: { Header(text: "Display") } footer: {
@@ -159,6 +165,42 @@ struct SettingsScreen: View {
     }
 }
 
+struct BackupCells: View {
+    private var g: AppGraph { .shared }
+    @State private var doc = ExportDocument()
+    @State private var exporting = false
+    @State private var importing = false
+    @State private var message: String?
+    @Environment(\.palette) private var p
+
+    var body: some View {
+        Button {
+            do { doc = ExportDocument(data: try StemifyExport.capture(g.stemPlaylists, g.settings).encoded()); exporting = true }
+            catch { message = error.localizedDescription }
+        } label: { ValueCell(title: "Export", value: "\(g.stemPlaylists.lists.count) playlists", icon: "square.and.arrow.up", iconBg: 0x007AFF) }
+            .themedRow()
+        Button { importing = true } label: { ValueCell(title: "Import", value: nil, icon: "square.and.arrow.down", iconBg: 0x34C759) }
+            .themedRow()
+            .fileExporter(isPresented: $exporting, document: doc, contentType: .json, defaultFilename: "Stemify \(Date().formatted(.iso8601.year().month().day()))") { r in
+                if case .failure(let e) = r { message = e.localizedDescription }
+            }
+            .fileImporter(isPresented: $importing, allowedContentTypes: [.json]) { r in
+                do {
+                    let url = try r.get()
+                    let scoped = url.startAccessingSecurityScopedResource()
+                    defer { if scoped { url.stopAccessingSecurityScopedResource() } }
+                    let x = try StemifyExport.decode(Data(contentsOf: url))
+                    let n = g.stemPlaylists.merge(x.playlists)
+                    x.apply(to: g.settings)
+                    message = "Imported \(n) playlist\(n == 1 ? "" : "s") and your sound settings."
+                } catch { message = error.localizedDescription }
+            }
+            .alert("Backup", isPresented: Binding(get: { message != nil }, set: { if !$0 { message = nil } })) {
+                Button("OK", role: .cancel) {}
+            } message: { Text(message ?? "") }
+    }
+}
+
 // ---- plex -----------------------------------------------------------------------------------
 
 struct PlexAccountScreen: View {