fix(tests): suppress ink_sparkle shader crash in integration test

The pre-compiled ink_sparkle.frag shader built for an earlier SDK version
causes an INVALID_ARGUMENT crash when rendered via software (LIBGL_ALWAYS_
SOFTWARE=1) in the CI Dagger container. Any button tap in the integration
test triggers an ink effect, which loads the shader and crashes.

Adding NoSplash.splashFactory to both app themes prevents the shader from
being loaded. This matches what helpers.dart already does for widget tests
and what CrashScreen does for its own MaterialApp.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/main.dart

@@ -109,6 +109,7 @@ class _SharedInboxAppState extends ConsumerState<SharedInboxApp> {
       theme: ThemeData(
         colorScheme: ColorScheme.fromSeed(seedColor: Colors.indigo),
         useMaterial3: true,
+        splashFactory: NoSplash.splashFactory,
       ),
       darkTheme: ThemeData(
         colorScheme: ColorScheme.fromSeed(
@@ -116,6 +117,7 @@ class _SharedInboxAppState extends ConsumerState<SharedInboxApp> {
           brightness: Brightness.dark,
         ),
         useMaterial3: true,
+        splashFactory: NoSplash.splashFactory,
       ),
       routerConfig: router,
     );