feat(a11y): color independence, reduce motion, reduce transparency (#21 phase 5)

Audit unchanged at 11 dark / 14 light — expected, as none of these
settings are exercised by performAccessibilityAudit, and simctl can
toggle only Increase Contrast, not Differentiate Without Color, Reduce
Motion, or Reduce Transparency. Correct by construction and build-clean;
runtime behaviour is verified in the Phase 6 manual pass.

Color independence:

- Widget status is now an SF Symbol (checkmark.circle.fill /
  exclamationmark.triangle.fill / exclamationmark.octagon.fill), the same
  vocabulary as the in-app badges, replacing a silent colour-only dot on
  both the domain rows and the small-view count pills. Status now survives
  greyscale and reads consistently across surfaces.
- Under accessibilityDifferentiateWithoutColor: the Dashboard
  summary-card dot becomes a per-filter symbol, the selected quick-filter
  chip gains a checkmark and a border (selection was fill-colour only, and
  also gains the .isSelected trait), and LabeledValueRow prefixes a
  warning/failure symbol. All gated on the setting so the default UI stays
  uncluttered.

Reduce motion: all five withAnimation/.animation sites now pass nil under
accessibilityReduceMotion — AppCopyButton's check cross-fade,
CollapsibleSectionView's expand/collapse, TimelineDiffView's scroll, and
WatchlistView's list reorder.

Reduce transparency: the single .thinMaterial capsule falls back to an
opaque AppSurfaceElevated fill under accessibilityReduceTransparency.

The SweepActivityController item from the plan is dropped: it is pure
ActivityKit lifecycle with no animation, confirmed back in the issue
triage.

1 files changed, 28 insertions, 2 deletions

diff --git a/DomainDig/ContentView.swift b/DomainDig/ContentView.swift
index bc159d9..ea6ead8 100644
--- a/DomainDig/ContentView.swift
+++ b/DomainDig/ContentView.swift
@@ -2580,6 +2580,7 @@ struct SectionTrustMetadataView: View {
 
 struct LabeledValueRow: View {
     @Environment(\.appDensity) private var appDensity
+    @Environment(\.accessibilityDifferentiateWithoutColor) private var differentiateWithoutColor
     let row: InfoRowViewData
 
     var body: some View {
@@ -2589,7 +2590,15 @@ struct LabeledValueRow: View {
                     Text(row.label)
                         .font(appDensity.font(.caption2))
                         .foregroundStyle(Color(.appTextSecondary))
-                    valueText
+                    HStack(alignment: .firstTextBaseline, spacing: 4) {
+                        if differentiateWithoutColor, let symbol = toneSymbol {
+                            Image(systemName: symbol)
+                                .font(appDensity.font(.caption2))
+                                .foregroundStyle(ResultColors.color(for: row.tone))
+                                .accessibilityHidden(true)
+                        }
+                        valueText
+                    }
                 }
                 .frame(maxWidth: .infinity, alignment: .leading)
                 .layoutPriority(1)
@@ -2602,6 +2611,17 @@ struct LabeledValueRow: View {
         .frame(minHeight: appDensity.metrics.rowMinHeight, alignment: .topLeading)
     }
 
+    /// A leading symbol for warning/failure tones, shown only under Differentiate
+    /// Without Color so tone is not conveyed by text colour alone. Hidden from
+    /// VoiceOver — the value text already carries the meaning.
+    private var toneSymbol: String? {
+        switch row.tone {
+        case .warning: return "exclamationmark.triangle.fill"
+        case .failure: return "xmark.octagon.fill"
+        default: return nil
+        }
+    }
+
     @ViewBuilder
     private var valueText: some View {
         let base = Text(row.value)
@@ -3588,6 +3608,7 @@ private struct DataPortabilitySettingsView: View {
 
 private struct DataManagementSettingsView: View {
     @Bindable var viewModel: DomainViewModel
+    @Environment(\.accessibilityReduceTransparency) private var reduceTransparency
 
     @State private var showClearHistoryConfirmation = false
     @State private var showClearCacheConfirmation = false
@@ -3695,7 +3716,12 @@ private struct DataManagementSettingsView: View {
                     .foregroundStyle(Color(.appTextSecondary))
                     .padding(.horizontal, 14)
                     .padding(.vertical, 10)
-                    .background(.thinMaterial, in: Capsule())
+                    // Reduce Transparency swaps the blur for an opaque surface.
+                    // On iOS 26+ the system also composites its own translucency
+                    // that the app cannot declare — verify there too (Phase 6).
+                    .background(
+                        Capsule().fill(reduceTransparency ? AnyShapeStyle(Color(.appSurfaceElevated)) : AnyShapeStyle(.thinMaterial))
+                    )
                     .padding(.bottom, 8)
                     .transition(.move(edge: .bottom).combined(with: .opacity))
             }