feat: enforce time and open limits in the background via Screen Time extensions

- Shared/ layer compiled into the app and three new extension targets:
  rule snapshots in the app group, the usage ledger, monitoring-plan
  naming, and LimitEnforcement (shared, unit-tested event reactions)
- RuleScheduler mirrors rules to the app group and reconciles
  DeviceActivity monitoring: one daily 00:00-23:59 activity per limit
  rule, with a cumulative usage-threshold event per budget minute for
  time limits; activities restart only when their configuration changes
  (a restart resets threshold accounting)
- OpenAppLockMonitor (DeviceActivityMonitor): midnight budget resets,
  records usage minutes, shields at the budget, re-shields when a
  granted open session ends
- OpenAppLockShieldConfig: open-limit shields show 'Opened X of N times
  today' with an 'Open (Y left)' secondary button
- OpenAppLockShieldAction: an Open press spends one open, lifts the
  rule's shield, and starts the ~15-minute one-shot session
- extensions are classic NSExtension app extensions (the ExtensionKit
  product type expects an @main entry and made the app fail to install);
  shield-store tracking moved to app-group defaults so the app and
  extensions see one consistent set
- maps iOS 26's new .approvedWithDataAccess authorization status to
  approved (it previously fell through @unknown default to notDetermined)
- shares the OpenAppLock scheme (Xcode dropped the autocreated one when
  targets were added)

Shared/RuleSchedule.swift

@@ -0,0 +1,89 @@
+//
+//  RuleSchedule.swift
+//  OpenAppLock
+//
+
+import Foundation
+
+/// The recurring time window of a rule, independent of any persistence.
+///
+/// A window whose end is at or before its start crosses midnight: 22:00 → 06:00
+/// starts on an enabled day and ends the following morning. `start == end`
+/// means a full 24-hour window.
+struct RuleSchedule: Hashable, Sendable {
+    var startMinutes: Int
+    var endMinutes: Int
+    var days: Set<Weekday>
+
+    var crossesMidnight: Bool { endMinutes <= startMinutes }
+
+    var durationMinutes: Int {
+        crossesMidnight
+            ? RuleSchedule.minutesPerDay - startMinutes + endMinutes
+            : endMinutes - startMinutes
+    }
+
+    /// The window containing `date`, if the schedule is active at that moment.
+    ///
+    /// Checks today's window and, for midnight-crossing schedules, the window
+    /// that started yesterday. The day a window *starts* on is the day that
+    /// must be enabled.
+    func activeWindow(containing date: Date, calendar: Calendar = .current) -> DateInterval? {
+        for dayOffset in [0, -1] {
+            guard
+                let day = calendar.date(byAdding: .day, value: dayOffset, to: date),
+                let window = window(onDayContaining: day, calendar: calendar),
+                window.start <= date, date < window.end
+            else { continue }
+            return window
+        }
+        return nil
+    }
+
+    func isActive(at date: Date, calendar: Calendar = .current) -> Bool {
+        activeWindow(containing: date, calendar: calendar) != nil
+    }
+
+    /// The next moment the schedule will begin a window strictly after `date`.
+    func nextStart(after date: Date, calendar: Calendar = .current) -> Date? {
+        guard !days.isEmpty else { return nil }
+        for dayOffset in 0...7 {
+            guard
+                let day = calendar.date(byAdding: .day, value: dayOffset, to: date),
+                let window = window(onDayContaining: day, calendar: calendar),
+                window.start > date
+            else { continue }
+            return window.start
+        }
+        return nil
+    }
+
+    /// The window starting on the given day, or nil when that weekday is not enabled.
+    private func window(onDayContaining day: Date, calendar: Calendar) -> DateInterval? {
+        let dayStart = calendar.startOfDay(for: day)
+        guard
+            let weekday = Weekday(rawValue: calendar.component(.weekday, from: dayStart)),
+            days.contains(weekday),
+            let start = calendar.date(byAdding: .minute, value: startMinutes, to: dayStart),
+            let end = calendar.date(
+                byAdding: .minute, value: startMinutes + durationMinutes, to: dayStart
+            )
+        else { return nil }
+        return DateInterval(start: start, end: end)
+    }
+
+    private static let minutesPerDay = 24 * 60
+}
+
+extension RuleSchedule {
+    /// "09:00" style label for a minutes-from-midnight value, matching the reference UI.
+    static func timeLabel(forMinutes minutes: Int) -> String {
+        let clamped = ((minutes % (24 * 60)) + 24 * 60) % (24 * 60)
+        return String(format: "%02d:%02d", clamped / 60, clamped % 60)
+    }
+
+    /// "09:00 – 17:00" range label used by rule details and preset cards.
+    var timeRangeLabel: String {
+        "\(Self.timeLabel(forMinutes: startMinutes)) – \(Self.timeLabel(forMinutes: endMinutes))"
+    }
+}