test: fix gamma default + localized home

Two tests asserted pre-refactor behavior:
- pen_config_test expected the old pressureGamma default of 1.0; it is
  now the natural curve (the pen-feel feature). Also assert the new
  eraser defaults.
- widget_test pumped HomeScreen without localization delegates, which
  the now-localized app bar requires. Provide the delegates.

Full suite: 258/258 pass.

test/widget_test.dart

@@ -3,6 +3,7 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
+import 'package:badnote/l10n/app_localizations.dart';
 import 'package:badnote/screens/home_screen.dart';
 
 void main() {
@@ -17,7 +18,14 @@ void main() {
     SharedPreferences.setMockInitialValues({});
 
     await tester.pumpWidget(
-      const ProviderScope(child: MaterialApp(home: HomeScreen())),
+      ProviderScope(
+        child: MaterialApp(
+          // The screen is now localized; provide the delegates it depends on.
+          localizationsDelegates: AppLocalizations.localizationsDelegates,
+          supportedLocales: AppLocalizations.supportedLocales,
+          home: const HomeScreen(),
+        ),
+      ),
     );
     await tester.pump();