feat(v3.6.0): add iCloud sharing for workflows and tracked domains

- implement CloudKit sharing (CKShare) for TrackedDomain and DomainWorkflow
- support read-only and editable permissions
- add Share actions and shared state indicators in UI
- handle shared record ownership and participant roles
- implement deterministic conflict resolution to prevent duplication
- ensure compatibility with existing iCloud sync layer
- maintain local-first behavior with graceful offline handling
- remove debug logging for domain availability/rdap messages

notes:
- no custom backend or accounts introduced
- sharing is Apple ecosystem only (iCloud-based)
- large history data remains local-only

1 files changed, 84 insertions, 0 deletions

diff --git a/DomainDig/CloudSharingSheet.swift b/DomainDig/CloudSharingSheet.swift
new file mode 100644
index 0000000..3d524ef
--- /dev/null
+++ b/DomainDig/CloudSharingSheet.swift
@@ -0,0 +1,84 @@
+import CloudKit
+import Foundation
+import SwiftUI
+import UIKit
+
+struct CloudSharingSheet: UIViewControllerRepresentable {
+    @Environment(\.dismiss) private var dismiss
+
+    let entity: ShareableEntity
+    let title: String
+
+    func makeCoordinator() -> Coordinator {
+        Coordinator(dismiss: dismiss, title: title)
+    }
+
+    func makeUIViewController(context: Context) -> UIViewController {
+        UIViewController()
+    }
+
+    func updateUIViewController(_ uiViewController: UIViewController, context: Context) {
+        context.coordinator.presentIfNeeded(from: uiViewController, entity: entity)
+    }
+
+    final class Coordinator: NSObject, UIAdaptivePresentationControllerDelegate {
+        private let dismissAction: DismissAction
+        private let title: String
+        private let observer = CKSystemSharingUIObserver(container: .default())
+        private var hasPresented = false
+
+        init(dismiss: DismissAction, title: String) {
+            self.dismissAction = dismiss
+            self.title = title
+            super.init()
+
+            observer.systemSharingUIDidSaveShareBlock = { _, _ in
+                Task { @MainActor in
+                    await CloudSyncService.shared.syncNow(trigger: .manual)
+                }
+            }
+
+            observer.systemSharingUIDidStopSharingBlock = { _, _ in
+                Task { @MainActor in
+                    await CloudSyncService.shared.syncNow(trigger: .manual)
+                }
+            }
+        }
+
+        func presentIfNeeded(from presenter: UIViewController, entity: ShareableEntity) {
+            guard !hasPresented else { return }
+            hasPresented = true
+
+            let itemProvider = NSItemProvider()
+            let container = CKContainer.default()
+
+            Task { @MainActor in
+                do {
+                    if let existingShare = try await CloudSyncService.shared.existingShare(for: entity) {
+                        itemProvider.registerCKShare(existingShare, container: container)
+                    } else {
+                        itemProvider.registerCKShare(container: container) {
+                            try await CloudSyncService.shared.createShare(for: entity)
+                        }
+                    }
+                } catch {
+                    dismissAction()
+                    return
+                }
+
+                let configuration = UIActivityItemsConfiguration(itemProviders: [itemProvider])
+                let activityController = UIActivityViewController(activityItemsConfiguration: configuration)
+                activityController.completionWithItemsHandler = { [dismissAction] _, _, _, _ in
+                    dismissAction()
+                }
+                activityController.popoverPresentationController?.sourceView = presenter.view
+                activityController.presentationController?.delegate = self
+                presenter.present(activityController, animated: true)
+            }
+        }
+
+        func presentationControllerDidDismiss(_ presentationController: UIPresentationController) {
+            dismissAction()
+        }
+    }
+}