feat: usar a cor escolhida tal e qual e opcao de suavizar

- TatuPalette.scheme aceita softenPrimary e passa a usar a seed como primary, onPrimary por contraste e surfaceTint, em vez da paleta tonal do Material 3
- nova opcao AppSettings.softenThemeColor (default false, ou seja cor exacta)
- interruptor 'Suavizar cor do tema' em Configuracoes > Aparencia, com l10n en/pt
- a opcao e sincronizada via account data (soften_theme_color) e mantida localmente como fallback, tal como a cor do tema
- setApplicationAccountColor e updateApplicationAccountConfig preservam o novo campo
- um unico sync de account data actualiza cor e opcao
- testes de serializacao e round-trip para o novo campo

test/account_config_test.dart

@@ -47,12 +47,14 @@ void main() {
         wallpaperOpacity: 0.3,
         wallpaperBlur: 4,
         primaryColor: 0xFF6750A4,
+        softenThemeColor: true,
       );
       final parsed = ApplicationAccountConfig.fromJson(config.toJson());
       expect(parsed.wallpaperUrl, config.wallpaperUrl);
       expect(parsed.wallpaperOpacity, config.wallpaperOpacity);
       expect(parsed.wallpaperBlur, config.wallpaperBlur);
       expect(parsed.primaryColor, config.primaryColor);
+      expect(parsed.softenThemeColor, config.softenThemeColor);
     });
 
     test('Keeps existing wallpaper defaults when parsing color only', () {
@@ -63,5 +65,50 @@ void main() {
       expect(config.wallpaperOpacity, 1);
       expect(config.wallpaperBlur, isNull);
     });
+
+    test('Parses soften theme color from account data', () {
+      expect(
+        ApplicationAccountConfig.fromJson({
+          'soften_theme_color': true,
+        }).softenThemeColor,
+        isTrue,
+      );
+      expect(
+        ApplicationAccountConfig.fromJson({
+          'soften_theme_color': false,
+        }).softenThemeColor,
+        isFalse,
+      );
+    });
+
+    test('Ignores soften theme color of unexpected type', () {
+      expect(
+        ApplicationAccountConfig.fromJson({
+          'soften_theme_color': 'yes',
+        }).softenThemeColor,
+        isNull,
+      );
+    });
+
+    test('Defaults soften theme color to null when absent', () {
+      expect(ApplicationAccountConfig.fromJson({}).softenThemeColor, isNull);
+    });
+
+    test('Serializes soften theme color', () {
+      const config = ApplicationAccountConfig(softenThemeColor: true);
+      expect(config.toJson()['soften_theme_color'], true);
+    });
+
+    test('Serializes missing soften theme color as null', () {
+      const config = ApplicationAccountConfig(primaryColor: 0xFF00D084);
+      expect(config.toJson()['soften_theme_color'], isNull);
+    });
+
+    test('Round trips soften theme color through json', () {
+      final parsed = ApplicationAccountConfig.fromJson(
+        const ApplicationAccountConfig(softenThemeColor: true).toJson(),
+      );
+      expect(parsed.softenThemeColor, isTrue);
+    });
   });
 }