Polish mobile onboarding and profile setup (#8438)

Originally stacked on #8375, now merged. Rebased onto main.

Polishes the onboarding landing page, community-link entry, and recovery
sheets. Profile setup uses a consistent sheet with a larger avatar,
inline display name, and draft photo/emoji/animated editing; iOS uses
native controls and coordinated avatar/sheet transitions.

Validation: mobile analysis, full tests, and normal pre-push checks
passed after rebase. Prior iOS build and device walkthrough passed;
native validation was not repeated after this rebase. Snapshots omitted
as requested.

---------

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

mobile/test/widget_test.dart

@@ -1,3 +1,4 @@
+import 'package:buzz/shared/hosted/hosted_environment.dart';
 import 'dart:async';
 import 'package:flutter/material.dart';
 import 'package:buzz/shared/community/paired_community_landing.dart';
@@ -100,7 +101,18 @@ void main() {
     );
     await tester.pump();
     expect(find.bySemanticsLabel('Buzz'), findsOneWidget);
-    expect(find.text('Scan a QR code'), findsOneWidget);
+    expect(
+      find.text('Sign in with builderlab'),
+      HostedEnvironment.enabled ? findsOneWidget : findsNothing,
+    );
+    expect(
+      find.text('Other options'),
+      HostedEnvironment.enabled ? findsOneWidget : findsNothing,
+    );
+    expect(
+      find.text('Scan a QR code'),
+      HostedEnvironment.enabled ? findsNothing : findsOneWidget,
+    );
   });
 }