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/Task/CompleteTaskView.swift

@@ -2,6 +2,11 @@ import SwiftUI
 import PhotosUI
 import ComposeApp
 
+/// Wrapper to retain the Kotlin ViewModel via @StateObject
+private class CompletionViewModelHolder: ObservableObject {
+    let vm = ComposeApp.TaskCompletionViewModel()
+}
+
 struct CompleteTaskView: View {
     let task: TaskResponse
     let onComplete: (TaskResponse?) -> Void  // Pass back updated task
@@ -9,7 +14,8 @@ struct CompleteTaskView: View {
     @Environment(\.dismiss) private var dismiss
     @StateObject private var taskViewModel = TaskViewModel()
     @StateObject private var contractorViewModel = ContractorViewModel()
-    private let completionViewModel = ComposeApp.TaskCompletionViewModel()
+    @StateObject private var completionHolder = CompletionViewModelHolder()
+    private var completionViewModel: ComposeApp.TaskCompletionViewModel { completionHolder.vm }
     @State private var completedByName: String = ""
     @State private var actualCost: String = ""
     @State private var notes: String = ""
@@ -200,7 +206,7 @@ struct CompleteTaskView: View {
                             }
                             .buttonStyle(.bordered)
                         }
-                        .onChange(of: selectedItems) { newItems in
+                        .onChange(of: selectedItems) { _, newItems in
                             Task {
                                 selectedImages = []
                                 for item in newItems {