Make contractor phone optional and add UI test accessibility identifiers

Updated contractor models and forms to make phone field optional. Added
accessibility identifiers for add buttons to enable UI testing.

Contractor changes:
- Kotlin: Made phone nullable in Contractor, ContractorCreateRequest,
  ContractorSummary models
- Android: Updated AddContractorDialog validation to only require name
- Android: Removed asterisk from phone field label
- Android: Updated ContractorDetailScreen to handle nullable phone
- iOS: Updated ContractorFormSheet validation to only check name field
- iOS: Updated form footer text to show only name as required
- iOS: Updated ContractorDetailView to use optional binding for phone display

Accessibility improvements:
- iOS: Added accessibility identifier to contractor add button in
  ContractorsListView
- iOS: Added accessibility identifier to task add button in
  ResidenceDetailView

These identifiers enable reliable UI testing by allowing tests to access
buttons by their accessibility identifiers instead of searching by label.

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

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

iosApp/iosApp/Residence/ResidenceDetailView.swift

@@ -56,9 +56,11 @@ struct ResidenceDetailView: View {
         
         .alert("Delete Residence", isPresented: $showDeleteConfirmation) {
             Button("Cancel", role: .cancel) { }
+                .accessibilityIdentifier(AccessibilityIdentifiers.Alert.cancelButton)
             Button("Delete", role: .destructive) {
                 deleteResidence()
             }
+            .accessibilityIdentifier(AccessibilityIdentifiers.Alert.deleteButton)
         } message: {
             if let residence = viewModel.selectedResidence {
                 Text("Are you sure you want to delete \(residence.name)? This action cannot be undone and will delete all associated tasks, documents, and data.")
@@ -223,6 +225,7 @@ private extension ResidenceDetailView {
                 Button("Edit") {
                     showEditResidence = true
                 }
+                .accessibilityIdentifier(AccessibilityIdentifiers.Residence.editButton)
             }
         }
     }
@@ -256,6 +259,7 @@ private extension ResidenceDetailView {
             } label: {
                 Image(systemName: "plus")
             }
+            .accessibilityIdentifier(AccessibilityIdentifiers.Task.addButton)
             
             if let residence = viewModel.selectedResidence, residence.isPrimaryOwner {
                 Button {
@@ -264,6 +268,7 @@ private extension ResidenceDetailView {
                     Image(systemName: "trash")
                         .foregroundStyle(.red)
                 }
+                .accessibilityIdentifier(AccessibilityIdentifiers.Residence.deleteButton)
             }
         }
     }