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.

SeveredUITests/OnboardingUITests.swift

@@ -0,0 +1,31 @@
+//
+//  OnboardingUITests.swift
+//  SeveredUITests
+//
+
+import XCTest
+
+final class OnboardingUITests: XCTestCase {
+    override func setUpWithError() throws {
+        continueAfterFailure = false
+    }
+
+    func testOnboardingWalksThroughPermissionToHome() throws {
+        let app = XCUIApplication.launchSevered(onboardingCompleted: false)
+
+        // Welcome step.
+        app.staticTexts["Severed"].waitToAppear()
+        app.buttons["onboardingContinueButton"].waitToAppear().tap()
+
+        // Permission step: granting (mocked) lands on the Apps home screen.
+        app.buttons["allowScreenTimeButton"].waitToAppear().tap()
+        app.buttons["newRuleButton"].waitToAppear()
+        XCTAssertTrue(app.staticTexts["Blocked Apps"].exists)
+    }
+
+    func testCompletedOnboardingIsSkipped() throws {
+        let app = XCUIApplication.launchSevered(onboardingCompleted: true)
+        app.buttons["newRuleButton"].waitToAppear()
+        XCTAssertFalse(app.buttons["onboardingContinueButton"].exists)
+    }
+}