Fade welcome bees with the QR scanner transition (#8859)

Fixes the welcome bees remaining visible when the QR scanner opens after
#8853. Bees now share the foreground’s fade and scale progress, pause
while hidden, and return on dismissal. Reduce Motion skips scaling.

Validated scanner open/close in the iPhone simulator,
normal/reduced-motion widget journeys, analysis, and the full mobile
suite. Simulator camera hardware is unavailable; QR decoding was not
exercised. Independent review found no blockers.


https://github.com/user-attachments/assets/1ce046b2-63e3-4441-90e9-9d9ec048bdfa

Signed-off-by: kenny lopez <klopez4212@gmail.com>
Co-authored-by: Terp <5856f6900e8e0a4e0ea1f4f8d2ee33e4753d2119bc122f94ecafc660b46c0511@buzz.block.builderlab.xyz>

mobile/lib/features/pairing/pairing_page.dart

@@ -365,6 +365,7 @@ class PairingPage extends HookConsumerWidget {
             value: onboardingSystemOverlayStyle,
             child: _OnboardingBackground(
               websiteWelcome: websiteWelcome,
+              scannerProgress: islandScannerProgress,
               child: Scaffold(
                 resizeToAvoidBottomInset:
                     hostedFlow?.stage != HostedFlowStage.profile,

mobile/lib/features/pairing/pairing_page/onboarding_background.dart

@@ -3,16 +3,21 @@ part of '../pairing_page.dart';
 class _OnboardingBackground extends StatelessWidget {
   final Widget child;
   final bool websiteWelcome;
+  final ValueListenable<double> scannerProgress;
 
   const _OnboardingBackground({
     required this.child,
     this.websiteWelcome = false,
+    this.scannerProgress = const AlwaysStoppedAnimation(0),
   });
 
   @override
   Widget build(BuildContext context) {
     if (websiteWelcome) {
-      return _WebsiteWelcomeBackground(child: child);
+      return _WebsiteWelcomeBackground(
+        scannerProgress: scannerProgress,
+        child: child,
+      );
     }
     final isDark = context._onboardingIsDark;
     return DecoratedBox(

mobile/lib/features/pairing/pairing_page/website_welcome_background.dart

@@ -4,8 +4,12 @@ part of '../pairing_page.dart';
 // The bee layer uses the website’s flight model and remains decorative.
 class _WebsiteWelcomeBackground extends HookWidget {
   final Widget child;
+  final ValueListenable<double> scannerProgress;
 
-  const _WebsiteWelcomeBackground({required this.child});
+  const _WebsiteWelcomeBackground({
+    required this.child,
+    required this.scannerProgress,
+  });
 
   @override
   Widget build(BuildContext context) {
@@ -29,11 +33,28 @@ class _WebsiteWelcomeBackground extends HookWidget {
                 Positioned.fill(
                   child: IgnorePointer(
                     child: ExcludeSemantics(
-                      child: LayoutBuilder(
-                        builder: (context, constraints) => RepaintBoundary(
-                          child: _WebsiteBeeSwarm(
-                            size: constraints.biggest,
-                            pointer: pointer,
+                      child: ValueListenableBuilder<double>(
+                        valueListenable: scannerProgress,
+                        builder: (context, progress, child) => Opacity(
+                          key: const Key('scanner-bees-opacity'),
+                          opacity: 1 - progress,
+                          child: Transform.scale(
+                            key: const Key('scanner-bees-scale'),
+                            scale: MediaQuery.disableAnimationsOf(context)
+                                ? 1
+                                : 1 - 0.04 * progress,
+                            child: TickerMode(
+                              enabled: progress < 1,
+                              child: child!,
+                            ),
+                          ),
+                        ),
+                        child: LayoutBuilder(
+                          builder: (context, constraints) => RepaintBoundary(
+                            child: _WebsiteBeeSwarm(
+                              size: constraints.biggest,
+                              pointer: pointer,
+                            ),
                           ),
                         ),
                       ),

mobile/test/features/pairing/pairing_qr_scanner_test.dart

@@ -317,6 +317,23 @@ void main() {
       await tester.pump();
       final opacity = find.byKey(const Key('scanner-welcome-opacity'));
       final scale = find.byKey(const Key('scanner-welcome-scale'));
+      void expectBeesMatchWelcome() {
+        if (adding) return;
+        expect(
+          tester
+              .widget<Opacity>(find.byKey(const Key('scanner-bees-opacity')))
+              .opacity,
+          tester.widget<Opacity>(opacity).opacity,
+        );
+        expect(
+          tester
+              .widget<Transform>(find.byKey(const Key('scanner-bees-scale')))
+              .transform
+              .storage[0],
+          tester.widget<Transform>(scale).transform.storage[0],
+        );
+      }
+
       // The welcome swarm animates continuously. Wait for the scanner's
       // observable transition endpoint rather than global frame idleness.
       Future<void> waitForOpacity(double target) async {
@@ -372,7 +389,9 @@ void main() {
           closeTo(1 - 0.04 * progress, 0.001),
         );
       }
+      expectBeesMatchWelcome();
       await waitForOpacity(0);
+      expectBeesMatchWelcome();
       expect(tester.widget<Opacity>(opacity).opacity, 0);
       expect(
         tester.widget<Transform>(scale).transform.storage[0],
@@ -390,6 +409,7 @@ void main() {
       await tester.tapAt(const Offset(196.5, 700));
       await tester.pump();
       await waitForOpacity(1);
+      expectBeesMatchWelcome();
       expect(tester.widget<Opacity>(opacity).opacity, 1);
       expect(tester.widget<Transform>(scale).transform.storage[0], 1);
       expect(