refactor: re-skin UI with native iOS components

Replace the Opal-style custom presentation with the bare iOS design
language, keeping the backend, flows, and accessibility identifiers:

- Home: NavigationStack + List; rules now presented as list rows with
  kind icon, block summary, and trailing live status; '+' in the toolbar
- New Rule: plain list of rule types and presets; editor still pushed
  via navigationDestination
- Editor: native Form (DatePicker rows, day circles with summary in the
  section header, toggle rows with footers, stepper rows); create
  commits with a prominent 'Add Rule' button replacing Hold to Commit;
  edit uses toolbar Done plus red Disable/Delete rows
- Detail: sheet with inline title + status caption, LabeledContent
  rows; Edit Rule pushes the editor natively
- Default color scheme: drop forced dark mode and custom tint; system
  appearance and accent throughout
- Delete Theme, HoldToCommitButton, RuleCardView and custom chrome
- Use concrete Color.primary/secondary in button row labels (the
  hierarchical styles resolve against the button tint)
- Tests: 93 passing; only delta is holdToCommitButton press →
  commitRuleButton tap in 5 call sites
- Spec: add §6 mapping the original presentation to the native one

Severed/Views/Components/DayOfWeekPicker.swift

@@ -5,29 +5,19 @@
 
 import SwiftUI
 
-/// "On these days:" — seven circular toggles (S M T W T F S) with a
-/// human-readable summary, as in the reference rule editors.
+/// Seven circular day toggles (S M T W T F S) using system colors, meant to
+/// sit inside a Form/List row. The day-set summary is shown by the enclosing
+/// section header.
 struct DayOfWeekPicker: View {
     @Binding var days: Set<Weekday>
 
     var body: some View {
-        VStack(alignment: .leading, spacing: 14) {
-            HStack {
-                Text("On these days:")
-                    .font(.system(size: 15, weight: .semibold))
-                Spacer()
-                Text(days.summary)
-                    .font(.system(size: 14))
-                    .foregroundStyle(Theme.textSecondary)
-            }
-            HStack(spacing: 8) {
-                ForEach(Weekday.displayOrder, id: \.self) { day in
-                    dayToggle(day)
-                }
+        HStack(spacing: 8) {
+            ForEach(Weekday.displayOrder, id: \.self) { day in
+                dayToggle(day)
             }
         }
-        .padding(16)
-        .background(Theme.surface, in: RoundedRectangle(cornerRadius: 18))
+        .padding(.vertical, 4)
     }
 
     private func dayToggle(_ day: Weekday) -> some View {
@@ -40,13 +30,16 @@ struct DayOfWeekPicker: View {
             }
         } label: {
             Text(day.shortLabel)
-                .font(.system(size: 15, weight: .semibold))
-                .foregroundStyle(isOn ? .black : Theme.textSecondary)
+                .font(.subheadline.weight(.semibold))
+                .foregroundStyle(isOn ? Color.white : .secondary)
                 .frame(maxWidth: .infinity)
                 .aspectRatio(1, contentMode: .fit)
-                .background(isOn ? Color.white : Theme.surfaceElevated, in: Circle())
+                .background(
+                    isOn ? AnyShapeStyle(.tint) : AnyShapeStyle(Color(.tertiarySystemFill)),
+                    in: Circle()
+                )
         }
-        .buttonStyle(.plain)
+        .buttonStyle(.borderless)
         .accessibilityIdentifier("dayToggle-\(day.rawValue)")
         .accessibilityLabel(day.abbreviation)
         .accessibilityAddTraits(isOn ? .isSelected : [])
@@ -55,7 +48,15 @@ struct DayOfWeekPicker: View {
 
 #Preview {
     @Previewable @State var days = Weekday.weekdays
-    DayOfWeekPicker(days: $days)
-        .padding()
-        .background(Theme.background)
+    Form {
+        Section {
+            DayOfWeekPicker(days: $days)
+        } header: {
+            HStack {
+                Text("On these days").textCase(nil)
+                Spacer()
+                Text(days.summary).textCase(nil)
+            }
+        }
+    }
 }