Add CloudKit sync for cross-device data persistence

- Switch CoreDataStack from NSPersistentContainer to NSPersistentCloudKitContainer
- Configure CloudKit container: iCloud.com.t-t.PlantGuide
- Remove uniqueness constraints from all Core Data entities (CloudKit incompatible)
- Add CloudKit container identifier to entitlements

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

PlantGuide/Data/DataSources/Local/CoreData/CoreDataStack.swift

@@ -6,6 +6,7 @@
 //  for plant identification iOS app.
 //
 
+import CloudKit
 import CoreData
 import Foundation
 
@@ -105,7 +106,7 @@ final class CoreDataStack: CoreDataStackProtocol, @unchecked Sendable {
     // - The coreDataQueue serializes any direct container operations
 
     /// The persistent container managing the Core Data stack
-    private let persistentContainer: NSPersistentContainer
+    private let persistentContainer: NSPersistentCloudKitContainer
 
     /// Serial queue for thread-safe operations
     private let coreDataQueue = DispatchQueue(label: "com.plantguide.coredata", qos: .userInitiated)
@@ -142,8 +143,8 @@ final class CoreDataStack: CoreDataStackProtocol, @unchecked Sendable {
     private static func createPersistentContainer(
         modelName: String,
         migrationConfig: MigrationConfiguration
-    ) -> NSPersistentContainer {
-        let container = NSPersistentContainer(name: modelName)
+    ) -> NSPersistentCloudKitContainer {
+        let container = NSPersistentCloudKitContainer(name: modelName)
 
         // Configure store description with migration options
         let storeDescription = container.persistentStoreDescriptions.first
@@ -154,6 +155,11 @@ final class CoreDataStack: CoreDataStackProtocol, @unchecked Sendable {
         storeDescription?.setOption(true as NSNumber, forKey: NSPersistentHistoryTrackingKey)
         storeDescription?.setOption(true as NSNumber, forKey: NSPersistentStoreRemoteChangeNotificationPostOptionKey)
 
+        // Configure CloudKit container
+        storeDescription?.cloudKitContainerOptions = NSPersistentCloudKitContainerOptions(
+            containerIdentifier: "iCloud.com.t-t.PlantGuide"
+        )
+
         container.loadPersistentStores { storeDescription, error in
             if let error = error as NSError? {
                 // Log the error - in production, consider recovery strategies

PlantGuide/Data/DataSources/Local/CoreData/PlantGuideModel.xcdatamodeld/PlantGuideModel.xcdatamodel/contents

@@ -19,11 +19,6 @@
         <relationship name="careSchedule" optional="YES" maxCount="1" deletionRule="Cascade" destinationEntity="CareScheduleMO" inverseName="plant" inverseEntity="CareScheduleMO"/>
         <relationship name="identifications" optional="YES" toMany="YES" deletionRule="Cascade" destinationEntity="IdentificationMO" inverseName="plant" inverseEntity="IdentificationMO"/>
         <relationship name="plantCareInfo" optional="YES" maxCount="1" deletionRule="Cascade" destinationEntity="PlantCareInfoMO" inverseName="plant" inverseEntity="PlantCareInfoMO"/>
-        <uniquenessConstraints>
-            <uniquenessConstraint>
-                <constraint value="id"/>
-            </uniquenessConstraint>
-        </uniquenessConstraints>
     </entity>
     <entity name="IdentificationMO" representedClassName="IdentificationMO" syncable="YES">
         <attribute name="confidenceScore" attributeType="Double" defaultValueString="0.0" usesScalarType="YES"/>
@@ -34,11 +29,6 @@
         <attribute name="longitude" optional="YES" attributeType="Double" defaultValueString="0.0" usesScalarType="NO"/>
         <attribute name="source" attributeType="String"/>
         <relationship name="plant" optional="YES" maxCount="1" deletionRule="Nullify" destinationEntity="PlantMO" inverseName="identifications" inverseEntity="PlantMO"/>
-        <uniquenessConstraints>
-            <uniquenessConstraint>
-                <constraint value="id"/>
-            </uniquenessConstraint>
-        </uniquenessConstraints>
     </entity>
     <entity name="CareScheduleMO" representedClassName="CareScheduleMO" syncable="YES">
         <attribute name="fertilizerSchedule" attributeType="String"/>
@@ -50,11 +40,6 @@
         <attribute name="wateringSchedule" attributeType="String"/>
         <relationship name="plant" optional="YES" maxCount="1" deletionRule="Nullify" destinationEntity="PlantMO" inverseName="careSchedule" inverseEntity="PlantMO"/>
         <relationship name="tasks" optional="YES" toMany="YES" deletionRule="Cascade" destinationEntity="CareTaskMO" inverseName="careSchedule" inverseEntity="CareTaskMO"/>
-        <uniquenessConstraints>
-            <uniquenessConstraint>
-                <constraint value="id"/>
-            </uniquenessConstraint>
-        </uniquenessConstraints>
     </entity>
     <entity name="CareTaskMO" representedClassName="CareTaskMO" syncable="YES">
         <attribute name="completedDate" optional="YES" attributeType="Date" usesScalarType="NO"/>
@@ -64,11 +49,6 @@
         <attribute name="scheduledDate" attributeType="Date" usesScalarType="NO"/>
         <attribute name="type" attributeType="String"/>
         <relationship name="careSchedule" optional="YES" maxCount="1" deletionRule="Nullify" destinationEntity="CareScheduleMO" inverseName="tasks" inverseEntity="CareScheduleMO"/>
-        <uniquenessConstraints>
-            <uniquenessConstraint>
-                <constraint value="id"/>
-            </uniquenessConstraint>
-        </uniquenessConstraints>
     </entity>
     <entity name="PlantCareInfoMO" representedClassName="PlantCareInfoMO" syncable="YES">
         <attribute name="additionalNotes" optional="YES" attributeType="String"/>
@@ -86,10 +66,5 @@
         <attribute name="trefleID" optional="YES" attributeType="Integer 32" defaultValueString="0" usesScalarType="YES"/>
         <attribute name="wateringScheduleData" attributeType="Binary"/>
         <relationship name="plant" optional="YES" maxCount="1" deletionRule="Nullify" destinationEntity="PlantMO" inverseName="plantCareInfo" inverseEntity="PlantMO"/>
-        <uniquenessConstraints>
-            <uniquenessConstraint>
-                <constraint value="id"/>
-            </uniquenessConstraint>
-        </uniquenessConstraints>
     </entity>
 </model>

PlantGuide/PlantGuide.entitlements

@@ -5,7 +5,9 @@
 	<key>aps-environment</key>
 	<string>development</string>
 	<key>com.apple.developer.icloud-container-identifiers</key>
-	<array/>
+	<array>
+		<string>iCloud.com.t-t.PlantGuide</string>
+	</array>
 	<key>com.apple.developer.icloud-services</key>
 	<array>
 		<string>CloudKit</string>