Add error dialogs with retry/cancel for network failures

Implemented user-friendly error handling for network call failures:

Android (Compose):
- Created reusable ErrorDialog component with retry and cancel buttons
- Updated TasksScreen to show error dialog popup instead of inline error
- Error dialog appears when network calls fail with option to retry

iOS (SwiftUI):
- Created ErrorAlertModifier and ErrorAlertInfo helpers
- Added .errorAlert() view modifier for consistent error handling
- Updated TaskFormView to show error alerts with retry/cancel options
- Error alerts appear when task creation or other network calls fail

Both platforms now provide a consistent user experience when network
errors occur, giving users the choice to retry the operation or cancel.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

iosApp/iosApp/Task/TaskFormView.swift

@@ -41,6 +41,9 @@ struct TaskFormView: View {
     @State private var titleError: String = ""
     @State private var residenceError: String = ""
 
+    // Error alert state
+    @State private var errorAlert: ErrorAlertInfo? = nil
+
     var body: some View {
         NavigationStack {
             ZStack {
@@ -173,6 +176,21 @@ struct TaskFormView: View {
                     isPresented = false
                 }
             }
+            .onChange(of: viewModel.errorMessage) { errorMessage in
+                if let errorMessage = errorMessage, !errorMessage.isEmpty {
+                    errorAlert = ErrorAlertInfo(message: errorMessage)
+                }
+            }
+            .errorAlert(
+                error: errorAlert,
+                onRetry: {
+                    errorAlert = nil
+                    submitForm()
+                },
+                onDismiss: {
+                    errorAlert = nil
+                }
+            )
         }
     }