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/RuleDraft.swift

@@ -0,0 +1,84 @@
+//
+//  RuleDraft.swift
+//  Severed
+//
+
+import Foundation
+
+/// Value-type working copy of a rule used by the editors, so cancelling an
+/// edit never touches the persisted model.
+struct RuleDraft: Equatable {
+    var name: String
+    var kind: RuleKind
+    var days: Set<Weekday>
+    var startMinutes: Int
+    var endMinutes: Int
+    var dailyLimitMinutes: Int
+    var maxOpens: Int
+    var hardMode: Bool
+    var selectionMode: SelectionMode
+    var selectionData: Data?
+    var selectionCount: Int
+
+    /// A fresh draft for a new rule of the given kind, using the reference
+    /// app's defaults (9–5 weekdays schedule, 45m/day, 5 opens/day).
+    init(kind: RuleKind) {
+        self.name = kind.defaultRuleName
+        self.kind = kind
+        self.days = Weekday.weekdays
+        self.startMinutes = 9 * 60
+        self.endMinutes = 17 * 60
+        self.dailyLimitMinutes = 45
+        self.maxOpens = 5
+        self.hardMode = false
+        self.selectionMode = .block
+        self.selectionData = nil
+        self.selectionCount = 0
+    }
+
+    init(rule: BlockingRule) {
+        self.name = rule.name
+        self.kind = rule.kind
+        self.days = rule.days
+        self.startMinutes = rule.startMinutes
+        self.endMinutes = rule.endMinutes
+        self.dailyLimitMinutes = rule.dailyLimitMinutes
+        self.maxOpens = rule.maxOpens
+        self.hardMode = rule.hardMode
+        self.selectionMode = rule.selectionMode
+        self.selectionData = rule.selectionData
+        self.selectionCount = rule.selectionCount
+    }
+
+    init(preset: RulePreset) {
+        self.init(kind: .schedule)
+        self.name = preset.name
+        self.days = preset.days
+        self.startMinutes = preset.startMinutes
+        self.endMinutes = preset.endMinutes
+    }
+
+    func apply(to rule: BlockingRule) {
+        rule.name = name
+        rule.kind = kind
+        rule.days = days
+        rule.startMinutes = startMinutes
+        rule.endMinutes = endMinutes
+        rule.dailyLimitMinutes = dailyLimitMinutes
+        rule.maxOpens = maxOpens
+        rule.hardMode = hardMode
+        rule.selectionMode = selectionMode
+        rule.selectionData = selectionData
+        rule.selectionCount = selectionCount
+    }
+
+    func makeRule() -> BlockingRule {
+        let rule = BlockingRule(name: name, kind: kind)
+        apply(to: rule)
+        return rule
+    }
+
+    var schedule: RuleSchedule {
+        RuleSchedule(startMinutes: startMinutes, endMinutes: endMinutes, days: days)
+    }
+}