fix(mobile): fill uploaded avatars on the Agents page (#8882)

Uploaded images on the mobile Agents page now crop to fill the avatar
squircle, matching desktop. Animated avatars and bundled character
posters retain their existing sizing.

Validation: `just mobile-check mobile-test` passed (4,050 Flutter tests;
34 skipped), plus before/after rendering of the production card.
Regression coverage checks uploaded, preset and animated images.

Snapshots use a sample rectangular PNG in a local Flutter widget
preview, not an installed build.

| Before | After |
| --- | --- |
| ![Uploaded PNG leaves gaps in the avatar
frame](https://github.com/user-attachments/assets/8f8591a1-48fd-4496-99e6-fd1c978c79bc)
| ![Uploaded PNG fills the avatar
squircle](https://github.com/user-attachments/assets/c7a3191f-2cd1-43ec-876a-baeb7896bb45)
|

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

mobile/lib/features/agents/agent_card.dart

@@ -45,6 +45,9 @@ class AgentCard extends StatelessWidget {
         style: context.textTheme.headlineMedium,
       ),
     );
+    final portraitFit = usesInsetAgentArtwork(imageUrl)
+        ? BoxFit.contain
+        : BoxFit.cover;
     final portrait =
         animation != null &&
             !MediaQuery.disableAnimationsOf(context) &&
@@ -52,12 +55,12 @@ class AgentCard extends StatelessWidget {
         ? ProgressiveAnimatedAvatar(
             descriptor: animation,
             fallback: fallback,
-            fit: BoxFit.contain,
+            fit: portraitFit,
           )
         : AvatarImageContent(
             imageUrl: poster,
             fallback: fallback,
-            fit: BoxFit.contain,
+            fit: portraitFit,
           );
     return ClipRRect(
       borderRadius: BorderRadius.circular(Radii.card),

mobile/test/features/agents/agent_card_grid_test.dart

@@ -3,11 +3,64 @@ import 'dart:ui' show SemanticsAction;
 import 'package:buzz/features/agents/agent_card.dart';
 import 'package:buzz/features/agents/agent_card_grid.dart';
 import 'package:buzz/shared/theme/theme.dart';
+import 'package:buzz/shared/widgets/avatar_image.dart';
+import 'package:buzz/shared/widgets/avatar_shape.dart';
+import 'package:buzz/shared/widgets/progressive_animated_avatar.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:hooks_riverpod/hooks_riverpod.dart';
 
 void main() {
+  testWidgets(
+    'uploaded portraits cover the frame while character artwork stays contained',
+    (tester) async {
+      for (final (url, expectedFit) in [
+        ('https://example.com/portrait.png', BoxFit.cover),
+        (
+          'https://dwwgwmfqqjotj.cloudfront.net/avatars/20260925T154625166Z/poster/pollies/pollies-10.png',
+          BoxFit.contain,
+        ),
+        (
+          'https://example.com/portrait.png#buzz-anim=https%3A%2F%2Fexample.com%2Fanimated.png',
+          BoxFit.contain,
+        ),
+      ]) {
+        await tester.pumpWidget(
+          ProviderScope(
+            child: MaterialApp(
+              theme: AppTheme.light(),
+              home: Center(
+                child: SizedBox(
+                  width: 180,
+                  height: 240,
+                  child: AgentCard(
+                    name: 'Portrait',
+                    imageUrl: url,
+                    onOpen: () {},
+                  ),
+                ),
+              ),
+            ),
+          ),
+        );
+        final portrait = find.descendant(
+          of: find.byType(AvatarClip),
+          matching: find.byType(AvatarImageContent),
+        );
+        expect(portrait, findsOneWidget);
+        expect(tester.widget<AvatarImageContent>(portrait).fit, expectedFit);
+        final animation = find.byType(ProgressiveAnimatedAvatar);
+        if (animation.evaluate().isNotEmpty) {
+          expect(
+            tester.widget<ProgressiveAnimatedAvatar>(animation).fit,
+            expectedFit,
+          );
+        }
+        expect(tester.takeException(), isNull);
+      }
+    },
+  );
+
   testWidgets('whole card opens profile without stealing footer taps', (
     tester,
   ) async {