Harden iOS app with audit fixes, UI consistency, and sheet race condition fixes

Applies verified fixes from deep audit (concurrency, performance, security,
accessibility), standardizes CRUD form buttons to Add/Save pattern, removes
.drawingGroup() that broke search bar TextFields, and converts vulnerable
.sheet(isPresented:) + if-let patterns to safe presentation to prevent
blank white modals.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

iosApp/iosApp/Contractor/ContractorFormSheet.swift

@@ -276,7 +276,7 @@ struct ContractorFormSheet: View {
                         if viewModel.isCreating || viewModel.isUpdating {
                             ProgressView()
                         } else {
-                            Text(contractor == nil ? L10n.Contractors.addButton : L10n.Common.save)
+                            Text(contractor == nil ? L10n.Common.add : L10n.Common.save)
                                 .bold()
                         }
                     }
@@ -297,6 +297,12 @@ struct ContractorFormSheet: View {
                 residenceViewModel.loadMyResidences()
                 loadContractorData()
             }
+            .onChange(of: residenceViewModel.selectedResidence?.id) { _, _ in
+                if let residence = residenceViewModel.selectedResidence,
+                   residence.id == selectedResidenceId {
+                    selectedResidenceName = residence.name
+                }
+            }
             .handleErrors(
                 error: viewModel.errorMessage,
                 onRetry: { saveContractor() }
@@ -440,11 +446,7 @@ struct ContractorFormSheet: View {
         if let residenceId = contractor.residenceId {
             selectedResidenceId = residenceId.int32Value
             if let selectedResidenceId {
-                ComposeApp.ResidenceViewModel().getResidence(id: selectedResidenceId, onResult: { result in
-                    if let success = result as? ApiResultSuccess<ResidenceResponse> {
-                        self.selectedResidenceName = success.data?.name
-                    }
-                })
+                residenceViewModel.getResidence(id: selectedResidenceId)
             }
         }