Integrate IndieBackup for snapshot backup and restore

Adds a local ZIP backup/restore of the iCloud document tree via the
IndieBackup package, surfaced in Settings with retention controls. A
restore suspends the sync observer, mirrors the files, then rebuilds the
SwiftData cache; opening a shared .workoutsbackup file restores it. The
engine exposes the container Documents root and a restore lifecycle
(isRestoring guards a concurrent connect), and the backup file type is
registered for open-in-place.

Claude-Session: https://claude.ai/code/session_01HJDQQDA9QdP8zByg43H5v3

Workouts/AppServices.swift

@@ -1,6 +1,7 @@
 import Foundation
 import Observation
 import SwiftData
+import IndieBackup
 
 /// Composition root for the iOS app. Owns the SwiftData cache container and the
 /// iCloud sync engine, and drives the one-shot launch sequence. Injected into the
@@ -10,6 +11,10 @@ import SwiftData
 final class AppServices {
     let container: ModelContainer
     let syncEngine: SyncEngine
+    /// Local ZIP backup/restore of the iCloud document tree (`backupRoot` = the
+    /// container's `Documents/`). Restores rebuild the SwiftData cache via
+    /// `SyncEngine.rebuildCache()`; see `AppBackupConfiguration`.
+    let backupController: BackupController
     let watchBridge: PhoneConnectivityBridge
     let workoutLauncher = WorkoutLauncher()
     let workoutHealthDeleter = WorkoutHealthDeleter()
@@ -26,7 +31,11 @@ final class AppServices {
     init() {
         let container = WorkoutsModelContainer.make()
         self.container = container
-        self.syncEngine = SyncEngine(container: container)
+        let syncEngine = SyncEngine(container: container)
+        self.syncEngine = syncEngine
+        self.backupController = BackupController(
+            configuration: AppBackupConfiguration(syncEngine: syncEngine)
+        )
         let liveRunState = LiveRunState()
         self.liveRunState = liveRunState
         self.watchBridge = PhoneConnectivityBridge(container: container, syncEngine: syncEngine, liveRunState: liveRunState)