feat: adult content filter toggle + native New Rule navigation

- Add Block Adult Content toggle to all three rule editors, persisted as
  BlockingRule.blockAdultContent (inline default for clean migration of
  existing stores) and surfaced in the detail sheet as an
  'Adult websites: Blocked/Allowed' row
- Engage Screen Time's adult-website filter
  (webContent.blockedByFilter = .auto()) alongside the rule's shield and
  clear it when the shield clears
- Replace the New Rule sheet's view-swap with a NavigationStack push
  (navigationDestination(item:)); the editor uses native chrome there
  (system back button, inline title, toolbar rename), enabling the push
  animation and edge-swipe back
- Tests: 93 passing (+2 unit: draft round-trip and enforcer forwarding;
  +3 UI: toggle-to-detail flow, default-allowed row, swipe-back as a
  behavioral proof of native navigation)
- Spec updated accordingly (editor sections, behavior, data model,
  navigation note)

Severed/Views/Rules/RuleEditorView.swift

@@ -16,7 +16,11 @@ struct RuleEditorView: View {
 
     let mode: Mode
     @State var draft: RuleDraft
-    var onBack: () -> Void
+    /// True when pushed inside a NavigationStack (New Rule flow): the editor
+    /// then uses native navigation chrome (system back button, swipe-back)
+    /// instead of its custom header.
+    var embedsInNavigationStack = false
+    var onBack: () -> Void = {}
     var onCommit: (RuleDraft) -> Void
     var onToggleEnabled: (() -> Void)?
     var onDelete: (() -> Void)?
@@ -26,8 +30,40 @@ struct RuleEditorView: View {
     @State private var renameText = ""
 
     var body: some View {
+        if embedsInNavigationStack {
+            core
+                .navigationBarTitleDisplayMode(.inline)
+                .toolbarBackground(.hidden, for: .navigationBar)
+                .toolbar {
+                    ToolbarItem(placement: .principal) {
+                        Text(draft.name)
+                            .font(.system(size: 18, weight: .semibold))
+                            .foregroundStyle(.white)
+                            .lineLimit(1)
+                            .accessibilityIdentifier("ruleEditorTitle")
+                    }
+                    ToolbarItem(placement: .topBarTrailing) {
+                        Button {
+                            renameText = draft.name
+                            showingRename = true
+                        } label: {
+                            Image(systemName: "pencil")
+                                .font(.system(size: 15, weight: .semibold))
+                                .foregroundStyle(.white)
+                        }
+                        .accessibilityIdentifier("renameButton")
+                    }
+                }
+        } else {
+            core
+        }
+    }
+
+    private var core: some View {
         VStack(spacing: 0) {
-            header
+            if !embedsInNavigationStack {
+                header
+            }
             ScrollView {
                 VStack(spacing: 18) {
                     sections
@@ -92,6 +128,7 @@ struct RuleEditorView: View {
             DayOfWeekPicker(days: $draft.days)
             appsSection(header: "Apps are blocked")
             hardModeSection
+            adultContentSection
         case .timeLimit:
             appsSection(header: "When I use")
             budgetSection(
@@ -104,6 +141,7 @@ struct RuleEditorView: View {
             DayOfWeekPicker(days: $draft.days)
             blockUntilSection
             hardModeSection
+            adultContentSection
         case .openLimit:
             appsSection(header: "When I open")
             budgetSection(
@@ -116,6 +154,7 @@ struct RuleEditorView: View {
             DayOfWeekPicker(days: $draft.days)
             blockUntilSection
             hardModeSection
+            adultContentSection
         }
     }
 
@@ -232,6 +271,25 @@ struct RuleEditorView: View {
         .background(Theme.surface, in: RoundedRectangle(cornerRadius: 18))
     }
 
+    private var adultContentSection: some View {
+        HStack {
+            VStack(alignment: .leading, spacing: 2) {
+                Text("Block Adult Content")
+                    .font(.system(size: 15, weight: .semibold))
+                Text("Filter adult websites while this rule is active")
+                    .font(.system(size: 12))
+                    .foregroundStyle(Theme.textTertiary)
+            }
+            Spacer()
+            Toggle("", isOn: $draft.blockAdultContent)
+                .labelsHidden()
+                .tint(Theme.accent)
+                .accessibilityIdentifier("adultContentToggle")
+        }
+        .padding(16)
+        .background(Theme.surface, in: RoundedRectangle(cornerRadius: 18))
+    }
+
     private func sectionHeader(systemImage: String, title: String) -> some View {
         HStack(spacing: 8) {
             Image(systemName: systemImage)