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/Contractor/ContractorFormSheet.swift

@@ -79,6 +79,7 @@ struct ContractorFormSheet: View {
                     }
                 } header: {
                     Text(L10n.Contractors.basicInfoSection)
+                        .accessibilityAddTraits(.isHeader)
                 } footer: {
                     Text(L10n.Contractors.basicInfoFooter)
                         .font(.caption)
@@ -155,6 +156,7 @@ struct ContractorFormSheet: View {
                     }
                 } header: {
                     Text(L10n.Contractors.contactInfoSection)
+                        .accessibilityAddTraits(.isHeader)
                 }
                 .sectionBackground()
 
@@ -226,6 +228,7 @@ struct ContractorFormSheet: View {
                     }
                 } header: {
                     Text(L10n.Contractors.addressSection)
+                        .accessibilityAddTraits(.isHeader)
                 }
                 .sectionBackground()