Add comprehensive accessibility identifiers for UI testing

Added AccessibilityIdentifiers helper struct with identifiers for all major
UI elements across the app. Applied identifiers throughout authentication,
navigation, forms, and feature screens to enable reliable UI testing.

Changes:
- Added Helpers/AccessibilityIdentifiers.swift with centralized ID definitions
- LoginView: Added identifiers for username, password, login button fields
- RegisterView: Added identifiers for registration form fields
- MainTabView: Added identifiers for all tab bar items
- ProfileTabView: Added identifiers for logout and settings buttons
- ResidencesListView: Added identifier for add button
- Task views: Added identifiers for add, save, and form fields
- Document forms: Added identifiers for form fields and buttons

Identifiers follow naming pattern: [Feature].[Element]
Example: AccessibilityIdentifiers.Authentication.loginButton

This enables UI tests to reliably locate elements using:
app.buttons[AccessibilityIdentifiers.Authentication.loginButton]

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

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

iosApp/iosApp/Task/AllTasksView.swift

@@ -142,6 +142,7 @@ struct AllTasksView: View {
                         .controlSize(.large)
                         .padding(.horizontal, 48)
                         .disabled(residenceViewModel.myResidences?.residences.isEmpty ?? true)
+                        .accessibilityIdentifier(AccessibilityIdentifiers.Task.addButton)
                         
                         if residenceViewModel.myResidences?.residences.isEmpty ?? true {
                             Text("Add a property first from the Residences tab")
@@ -225,6 +226,7 @@ struct AllTasksView: View {
                     Image(systemName: "plus")
                 }
                 .disabled(residenceViewModel.myResidences?.residences.isEmpty ?? true)
+                .accessibilityIdentifier(AccessibilityIdentifiers.Task.addButton)
             }
             
             ToolbarItem(placement: .navigationBarTrailing) {