refactor: splash nextScreen as constructor param instead of mutable static

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

lib/ui/screens/splash_screen.dart

@@ -2,15 +2,17 @@ import 'package:flutter/material.dart';
 
 import 'home_screen.dart';
 
+Widget _defaultNextScreen() => const HomeScreen();
+
 /// Logo-assembly splash: four glossy blocks fly in to form a 2x2 mark, the
 /// wordmark fades in, then we hand off. SaveRepository is already opened in
 /// main() so this doubles as perceived-zero loading time.
 class SplashScreen extends StatefulWidget {
-  const SplashScreen({super.key});
+  const SplashScreen({super.key, this.nextScreen = _defaultNextScreen});
 
-  /// Where the splash goes when finished; the season title card task
-  /// repoints this.
-  static Widget Function() nextScreen = () => const HomeScreen();
+  /// Built when the splash finishes; the season title card task repoints
+  /// the default.
+  final Widget Function() nextScreen;
 
   @override
   State<SplashScreen> createState() => _SplashScreenState();
@@ -24,7 +26,7 @@ class _SplashScreenState extends State<SplashScreen>
   )..addStatusListener((status) {
       if (status == AnimationStatus.completed && mounted) {
         Navigator.of(context).pushReplacement(
-          MaterialPageRoute(builder: (_) => SplashScreen.nextScreen()),
+          MaterialPageRoute(builder: (_) => widget.nextScreen()),
         );
       }
     });