fix(tests): suppress ink_sparkle shader crash in software rendering

Integration tests under software rendering (LIBGL_ALWAYS_SOFTWARE=1)
crash with an INVALID_ARGUMENT error when the Material 3 ink_sparkle
ripple shader is compiled. Disable it via splashFactory: NoSplash.

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,
     );