iOS VoiceOver accessibility overhaul — 67 files

New framework:
- AccessibilityLabels.swift: centralized A11y struct with VoiceOver strings
- AccessibilityModifiers.swift: reusable .a11yHeader, .a11yDecorative,
  .a11yButton, .a11yCard, .a11yStatValue View extensions

Shared components: decorative elements hidden, stat views combined,
status/priority badges labeled, error views announced, empty states grouped

Cards: ResidenceCard, TaskCard, DynamicTaskCard, ContractorCard,
DocumentCard, WarrantyCard — all grouped with combined labels,
chevrons hidden, action buttons labeled

Main screens: Login, Register, Residences, Tasks, Contractors, Documents —
toolbar buttons labeled, section headers marked, form field hints added

Onboarding: all 10 views — header traits, button hints, task selection
state, progress indicator, decorative backgrounds hidden

Profile/Subscription: toggle hints, theme selection state, feature
comparison table accessibility, subscription button labels

iOS build verified: BUILD SUCCEEDED

iosApp/iosApp/Onboarding/OnboardingCoordinator.swift

@@ -197,6 +197,7 @@ struct OnboardingCoordinator: View {
                         .foregroundColor(Color.appPrimary)
                 }
                 .accessibilityIdentifier(AccessibilityIdentifiers.Onboarding.backButton)
+                .accessibilityLabel("Go back")
                 .frame(width: 44, alignment: .leading)
                 .opacity(showBackButton ? 1 : 0)
                 .disabled(!showBackButton)
@@ -207,6 +208,7 @@ struct OnboardingCoordinator: View {
                 if showProgressIndicator {
                     OnboardingProgressIndicator(currentStep: currentProgressStep, totalSteps: 5)
                         .accessibilityIdentifier(AccessibilityIdentifiers.Onboarding.progressIndicator)
+                        .accessibilityLabel("Step \(currentProgressStep + 1) of 5")
                 }
 
                 Spacer()
@@ -219,6 +221,7 @@ struct OnboardingCoordinator: View {
                         .foregroundColor(Color.appTextSecondary)
                 }
                 .accessibilityIdentifier(AccessibilityIdentifiers.Onboarding.skipButton)
+                .accessibilityLabel("Skip")
                 .frame(width: 44, alignment: .trailing)
                 .opacity(showSkipButton ? 1 : 0)
                 .disabled(!showSkipButton)