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/Views/Components/HoldToCommitButton.swift

@@ -0,0 +1,54 @@
+//
+//  HoldToCommitButton.swift
+//  Severed
+//
+
+import SwiftUI
+
+/// The deliberate-friction commit button: the user must press and hold for a
+/// second to save a rule, mirroring the reference app's "Hold to Commit".
+struct HoldToCommitButton: View {
+    var title = "Hold to Commit"
+    var holdDuration: Double = 1.0
+    let action: () -> Void
+
+    @State private var progress: Double = 0
+
+    var body: some View {
+        ZStack {
+            RoundedRectangle(cornerRadius: 28)
+                .fill(Theme.surfaceElevated)
+            GeometryReader { proxy in
+                RoundedRectangle(cornerRadius: 28)
+                    .fill(Theme.commitGradient)
+                    .opacity(0.85)
+                    .frame(width: proxy.size.width * progress)
+                    .animation(.linear(duration: 0.1), value: progress == 0)
+            }
+            Text(title)
+                .font(.system(size: 17, weight: .semibold))
+                .foregroundStyle(.white)
+        }
+        .frame(height: 56)
+        .clipShape(RoundedRectangle(cornerRadius: 28))
+        .contentShape(RoundedRectangle(cornerRadius: 28))
+        .onLongPressGesture(minimumDuration: holdDuration) {
+            progress = 0
+            action()
+        } onPressingChanged: { pressing in
+            withAnimation(.linear(duration: pressing ? holdDuration : 0.2)) {
+                progress = pressing ? 1 : 0
+            }
+        }
+        .accessibilityElement(children: .ignore)
+        .accessibilityAddTraits(.isButton)
+        .accessibilityIdentifier("holdToCommitButton")
+        .accessibilityLabel(title)
+    }
+}
+
+#Preview {
+    HoldToCommitButton { }
+        .padding()
+        .background(Theme.background)
+}