feat: clone Opal's rules feature with hard block enforcement

Rebuild the app around recurring screen-time blocking rules modeled on
Opal's My Apps tab:

- Onboarding with FamilyControls Screen Time authorization
- Apps home with Blocked Apps tiles and live rule cards
- New Rule sheet: Schedule/Time Limit/Open Limit types + preset gallery
- Rule editors: time windows (incl. overnight), day picker, app selection
  via FamilyActivityPicker (Block/Allow Only), rename, Hold to Commit
- Hard Mode: active hard rules cannot be edited, disabled, deleted, or
  unblocked until their window ends; soft rules pause until next window
- Shield enforcement through per-rule ManagedSettingsStore + RuleEnforcer
- 73 unit tests (Swift Testing) + 16 UI tests (XCUITest) with launch-arg
  harness for in-memory storage, mocked authorization, seeded scenarios
- docs/RULES_FEATURE_SPEC.md: spec derived from the reference recording

Known gap: background window transitions and time/open-limit thresholds
need a DeviceActivityMonitor extension; shields currently sync while the
app is running.

Severed/Models/RulePreset.swift

@@ -0,0 +1,98 @@
+//
+//  RulePreset.swift
+//  Severed
+//
+
+import SwiftUI
+
+/// A suggested schedule rule shown in the New Rule sheet's preset gallery,
+/// mirroring the reference app's sections and timings.
+struct RulePreset: Identifiable, Hashable, Sendable {
+    let id: String
+    let name: String
+    let startMinutes: Int
+    let endMinutes: Int
+    let days: Set<Weekday>
+    let symbolName: String
+    /// Gradient stand-in for the reference app's photo backgrounds.
+    let gradientTop: Color
+    let gradientBottom: Color
+
+    var schedule: RuleSchedule {
+        RuleSchedule(startMinutes: startMinutes, endMinutes: endMinutes, days: days)
+    }
+}
+
+/// A titled group of presets ("Get More Done", "Sleep, Relax and Reset", …).
+struct RulePresetSection: Identifiable, Hashable, Sendable {
+    let id: String
+    let title: String
+    let subtitle: String
+    let presets: [RulePreset]
+
+    static let all: [RulePresetSection] = [
+        RulePresetSection(
+            id: "productivity",
+            title: "Get More Done",
+            subtitle: "Maximize your productivity while staying sane.",
+            presets: [
+                RulePreset(
+                    id: "work-time", name: "Work Time",
+                    startMinutes: 9 * 60, endMinutes: 17 * 60, days: Weekday.weekdays,
+                    symbolName: "briefcase.fill",
+                    gradientTop: Color(red: 0.16, green: 0.27, blue: 0.22),
+                    gradientBottom: Color(red: 0.05, green: 0.10, blue: 0.08)
+                ),
+                RulePreset(
+                    id: "laser-focus", name: "Laser Focus",
+                    startMinutes: 14 * 60, endMinutes: 18 * 60, days: Weekday.weekdays,
+                    symbolName: "scope",
+                    gradientTop: Color(red: 0.13, green: 0.20, blue: 0.33),
+                    gradientBottom: Color(red: 0.04, green: 0.06, blue: 0.12)
+                ),
+            ]
+        ),
+        RulePresetSection(
+            id: "sleep",
+            title: "Sleep, Relax and Reset",
+            subtitle: "Sleep better, rise refreshed.",
+            presets: [
+                RulePreset(
+                    id: "wind-down", name: "Wind Down",
+                    startMinutes: 20 * 60, endMinutes: 22 * 60, days: Weekday.everyDay,
+                    symbolName: "moon.haze.fill",
+                    gradientTop: Color(red: 0.25, green: 0.18, blue: 0.33),
+                    gradientBottom: Color(red: 0.08, green: 0.05, blue: 0.12)
+                ),
+                RulePreset(
+                    id: "deep-sleep", name: "Deep Sleep",
+                    startMinutes: 22 * 60, endMinutes: 6 * 60, days: Weekday.everyDay,
+                    symbolName: "moon.zzz.fill",
+                    gradientTop: Color(red: 0.10, green: 0.13, blue: 0.30),
+                    gradientBottom: Color(red: 0.02, green: 0.03, blue: 0.10)
+                ),
+            ]
+        ),
+        RulePresetSection(
+            id: "habits",
+            title: "Build Healthy Habits",
+            subtitle: "Spend time on important things.",
+            presets: [
+                RulePreset(
+                    id: "reading-time", name: "Reading Time",
+                    startMinutes: 19 * 60 + 45, endMinutes: 20 * 60 + 45, days: Weekday.everyDay,
+                    symbolName: "book.fill",
+                    gradientTop: Color(red: 0.33, green: 0.23, blue: 0.13),
+                    gradientBottom: Color(red: 0.12, green: 0.07, blue: 0.03)
+                ),
+                RulePreset(
+                    id: "gym-time", name: "Gym Time",
+                    startMinutes: 17 * 60 + 30, endMinutes: 18 * 60 + 30, days: Weekday.everyDay,
+                    symbolName: "figure.run",
+                    gradientTop: Color(red: 0.13, green: 0.30, blue: 0.30),
+                    gradientBottom: Color(red: 0.03, green: 0.10, blue: 0.10)
+                ),
+            ]
+        ),
+    ]
+}