feat(a11y): semantic colour system (#21 phase 1)

Replaces every hard-coded colour with semantic asset colours that adapt to
light, dark, and Increase Contrast. Dark mode stays locked, so this is a
pure refactor: the audit reports the same findings before and after.

The accent is now blue rather than cyan, per the tech/DNS theme.

Why custom values rather than the system palette: every system colour
fails WCAG AA in light mode. Measured on white — systemYellow 1.51:1,
systemOrange 2.20:1, systemGreen 2.22:1, systemCyan 2.54:1, systemRed
3.55:1. All of them pass in dark mode, which is why the dark-locked app
looked fine, and why unlocking light mode was never a matter of deleting
.preferredColorScheme(.dark). Every new value clears 4.5:1 as text on its
page, its card, and its own 16% badge tint — the way AppStatusBadgeView
actually draws it.

The accent needed splitting in two. As text on a dark background it must
be light; as a fill behind a white label it must be dark. #4DA3FF reads
8.00:1 as text on black but 2.63:1 behind white text, so StatusInfo /
AccentColor cover the foreground role and AccentFill covers
.borderedProminent. AppOnAccent is the label colour for a solid fill and
flips by scheme.

Colours live in Shared/Colors.xcassets rather than the app catalog: the
Shared folder is already a synchronized group in all three targets, so
the widget and share extension pick the palette up with no project-file
surgery. AccentColor stays in the app catalog as the global tint — and is
now actually defined, having been an empty colorset that silently left
system controls rendering in stock blue while custom chrome used cyan.

Two deliberate visual changes: orange folds into StatusWarning and pink
into StatusCritical. They encoded the same severity as the colours they
now share, and both sites also carry a text label.

Audit findings drop 15 to 14, and one of the originals turned out to be
a phantom: the Inspect contrast failure was the Run button in its
disabled state, which WCAG 1.4.3 exempts. testInspectScreen now types a
domain first so the audit measures an enabled control. Findings also
carry the offending element now, so the remaining clipped-text items name
themselves ("No Portfolio Yet", "Search domains") instead of being
anonymous.

1 files changed, 9 insertions, 9 deletions

diff --git a/DomainDig/HistoryView.swift b/DomainDig/HistoryView.swift
index 5350168..ffa7745 100644
--- a/DomainDig/HistoryView.swift
+++ b/DomainDig/HistoryView.swift
@@ -25,7 +25,7 @@ struct HistoryView: View {
                     systemImage: "clock.arrow.trianglehead.counterclockwise.rotate.90",
                     showsCardBackground: false
                 )
-                    .listRowBackground(Color(.systemGray6).opacity(0.5))
+                    .listRowBackground(Color(.appSurface))
             } else {
                 Section("Domains") {
                     ForEach(domainSummaries, id: \.domain) { item in
@@ -55,21 +55,21 @@ struct HistoryView: View {
                                             model: .init(
                                                 title: severity.title,
                                                 systemImage: "arrow.triangle.2.circlepath",
-                                                foregroundColor: severity == .high ? .red : .yellow,
-                                                backgroundColor: (severity == .high ? Color.red : .yellow).opacity(0.16)
+                                                foregroundColor: severity == .high ? Color(.statusCritical) : Color(.statusWarning),
+                                                backgroundColor: (severity == .high ? Color(.statusCritical) : Color(.statusWarning)).opacity(0.16)
                                             )
                                         )
                                     }
                                 }
                             }
                         }
-                        .listRowBackground(Color(.systemGray6).opacity(0.5))
+                        .listRowBackground(Color(.appSurface))
                     }
                 }
             }
         }
         .scrollContentBackground(.hidden)
-        .background(Color.black)
+        .background(Color(.appBackground))
         .navigationTitle("History")
         .searchable(text: $viewModel.timelineDomainFilter, prompt: "Search domains")
         .toolbar {
@@ -321,7 +321,7 @@ struct HistoryDetailView: View {
             .padding(.horizontal)
             .padding(.bottom, 32)
         }
-        .background(Color.black)
+        .background(Color(.appBackground))
         .navigationTitle(entry.domain)
         .toolbar {
             ToolbarItemGroup(placement: .topBarTrailing) {
@@ -390,12 +390,12 @@ struct HistoryDetailView: View {
             if let mismatchNote = viewModel.resolverMismatchNote(for: entry) {
                 Text(mismatchNote)
                     .font(appDensity.font(.caption2))
-                    .foregroundStyle(.orange)
+                    .foregroundStyle(Color(.statusWarning))
             }
             if entry.isPartialSnapshot {
                 Text("Partial snapshot: \(entry.validationIssues.joined(separator: " | "))")
                     .font(appDensity.font(.caption2))
-                    .foregroundStyle(.yellow)
+                    .foregroundStyle(Color(.statusWarning))
             }
             if let note = entry.note, !note.isEmpty {
                 Text(note)
@@ -406,7 +406,7 @@ struct HistoryDetailView: View {
         .foregroundStyle(.secondary)
         .padding(8)
         .frame(maxWidth: .infinity, alignment: .leading)
-        .background(Color(.systemGray6).opacity(0.3))
+        .background(Color(.appSurface))
         .clipShape(RoundedRectangle(cornerRadius: appDensity.metrics.cardCornerRadius))
         .padding(.vertical, 12)
     }