fix app lock hanging on macOS and blocking the photo picker

- Lock only when the scene really backgrounds: transient inactive
  states (system photo picker, app switcher) no longer swap in the
  lock screen and break gallery selection on iOS.
- Cache biometric availability once per session off the main thread
  instead of calling LAContext.canEvaluatePolicy in view bodies,
  which froze the macOS lock screen, and auto-prompt biometrics on
  iOS only.
- Keep UI tests as an opt-in target and guard both fixes in
  verify.sh.

Sources/App/LumaApp.swift

@@ -11,7 +11,20 @@ struct LumaApp: App {
             RootView(model: model)
                 .tint(Color(red: 0.14, green: 0.56, blue: 0.96))
                 .onChange(of: scenePhase) { _, phase in
-                    model.setApplicationActive(phase == .active)
+                    switch phase {
+                    case .active:
+                        model.setApplicationActive(true)
+                    case .background:
+                        model.setApplicationActive(false)
+                    case .inactive:
+                        // App switcher, Control Center and system pickers
+                        // (photo gallery) make the scene briefly inactive;
+                        // locking here would block the picker and the
+                        // unlock screen would replace the app mid-flow.
+                        break
+                    @unknown default:
+                        break
+                    }
                 }
         }
 #if os(macOS)