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.

Co-Authored-By: Claude <noreply@anthropic.com>

Severed/Models/BlockingRule.swift

@@ -0,0 +1,91 @@
+//
+//  BlockingRule.swift
+//  Severed
+//
+
+import Foundation
+import SwiftData
+
+/// A recurring screen-time blocking rule.
+///
+/// Times are stored as minutes from midnight so the schedule repeats cleanly and
+/// is independent of time zones at creation. A window whose end is at or before
+/// its start (e.g. 22:00 → 06:00) crosses midnight into the following day.
+@Model
+final class BlockingRule {
+    @Attribute(.unique) var id: UUID
+    var name: String
+    var kindRaw: String
+    var isEnabled: Bool
+    /// Hard block: while the rule is active it cannot be disabled, edited, or unblocked.
+    var hardMode: Bool
+    var selectionModeRaw: String
+    /// Encoded `FamilyActivitySelection` (opaque tokens). Nil until the user picks apps.
+    var selectionData: Data?
+    /// Denormalized count of selected apps/categories/domains for display.
+    var selectionCount: Int
+    var dayNumbers: [Int]
+    var startMinutes: Int
+    var endMinutes: Int
+    /// Daily usage budget for `.timeLimit` rules.
+    var dailyLimitMinutes: Int
+    /// Daily open budget for `.openLimit` rules.
+    var maxOpens: Int
+    /// When set, the rule's current window is suspended (user tapped Unblock).
+    /// Cleared automatically once the date passes; never set while Hard Mode is active.
+    var pausedUntil: Date?
+    var createdAt: Date
+
+    init(
+        id: UUID = UUID(),
+        name: String,
+        kind: RuleKind = .schedule,
+        isEnabled: Bool = true,
+        hardMode: Bool = false,
+        selectionMode: SelectionMode = .block,
+        selectionData: Data? = nil,
+        selectionCount: Int = 0,
+        days: Set<Weekday> = Weekday.weekdays,
+        startMinutes: Int = 9 * 60,
+        endMinutes: Int = 17 * 60,
+        dailyLimitMinutes: Int = 45,
+        maxOpens: Int = 5,
+        pausedUntil: Date? = nil,
+        createdAt: Date = .now
+    ) {
+        self.id = id
+        self.name = name
+        self.kindRaw = kind.rawValue
+        self.isEnabled = isEnabled
+        self.hardMode = hardMode
+        self.selectionModeRaw = selectionMode.rawValue
+        self.selectionData = selectionData
+        self.selectionCount = selectionCount
+        self.dayNumbers = days.map(\.rawValue).sorted()
+        self.startMinutes = startMinutes
+        self.endMinutes = endMinutes
+        self.dailyLimitMinutes = dailyLimitMinutes
+        self.maxOpens = maxOpens
+        self.pausedUntil = pausedUntil
+        self.createdAt = createdAt
+    }
+
+    var kind: RuleKind {
+        get { RuleKind(rawValue: kindRaw) ?? .schedule }
+        set { kindRaw = newValue.rawValue }
+    }
+
+    var selectionMode: SelectionMode {
+        get { SelectionMode(rawValue: selectionModeRaw) ?? .block }
+        set { selectionModeRaw = newValue.rawValue }
+    }
+
+    var days: Set<Weekday> {
+        get { Set(dayNumbers.compactMap(Weekday.init(rawValue:))) }
+        set { dayNumbers = newValue.map(\.rawValue).sorted() }
+    }
+
+    var schedule: RuleSchedule {
+        RuleSchedule(startMinutes: startMinutes, endMinutes: endMinutes, days: days)
+    }
+}