2.0: CloudKit private-database sync replaces KV snapshot sync

Foundation for 2.1 family sharing (CKShare needs these models + container).
SwiftData cannot share across Apple IDs today, so 2.0 ships true multi-device
sync for the same account instead:

- Models made CloudKit-compatible: dropped @Attribute(.unique) on all 5,
  inline defaults on every attribute, WeekPlan.slots stored as optional
  relationship (name preserved → lightweight migration) with non-optional
  slotList facade; ~73 call sites renamed.
- Container: cloudKitDatabase .automatic, falling back to the local-only
  store when CloudKit is unavailable; failures recorded to Crashlytics.
- Entitlements: iCloud CloudKit service (container already existed);
  remote-notification background mode for push-driven sync.
- Legacy KV snapshot sync (ICloudSyncService) stays inert when CloudKit is
  active — kept only for 1.x devices.
- DeduplicationService collapses cross-device duplicates deterministically on
  launch (settings singleton, default tags with tagId remapping, same-week
  plans).
- Note: AppSettings.isPremium now syncs across same-Apple-ID devices; StoreKit
  (PremiumSyncService + Transaction.updates) remains the source of truth and
  reconciles on every launch/foreground.

All 21 unit tests pass, including ICloudSyncPremiumIsolationTests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BkanrydYtrme8wipTzWssG

MealMood/MealMoodApp.swift

@@ -6,6 +6,14 @@ import FirebaseCrashlytics
 import GoogleMobileAds
 #endif
 
+/// Whether the store is syncing through CloudKit this launch. When true, the
+/// legacy iCloud KV snapshot sync must stay inert (both would fight).
+enum CloudSyncRuntime {
+    // Written exactly once during app start (before any concurrency), then
+    // read-only for the rest of the launch.
+    nonisolated(unsafe) static var isCloudKitActive = false
+}
+
 @main
 struct MealMoodApp: App {
     private let modelContainer: ModelContainer = {
@@ -17,6 +25,20 @@ struct MealMoodApp: App {
             MealSlot.self,
             ShoppingItem.self
         ])
+
+        // 2.0: CloudKit private-database sync (multi-device, same Apple ID).
+        // Falls back to the local-only store when CloudKit isn't available
+        // (signed-out iCloud, missing entitlement in dev builds, etc.).
+        let cloudConfiguration = ModelConfiguration(cloudKitDatabase: .automatic)
+        do {
+            let container = try ModelContainer(for: schema, configurations: [cloudConfiguration])
+            CloudSyncRuntime.isCloudKitActive = true
+            return container
+        } catch {
+            CrashlyticsService.record(error, context: "cloudkit_container")
+            print("CloudKit container unavailable, using local store: \(error)")
+        }
+
         let configuration = ModelConfiguration(cloudKitDatabase: .none)
         do {
             return try ModelContainer(for: schema, configurations: [configuration])