feat: sincronizar cor do tema via account data da conta Matrix

A cor escolhida no Appearance passa a ser guardada em im.fluffychat.account_config (primary_color), em vez de apenas nas preferencias locais do dispositivo.

- ApplicationAccountConfig ganha primaryColor, preservado em updateApplicationAccountConfig e no novo setApplicationAccountColor
- ThemeController restaura a cor da conta activa, aguarda accountDataLoading e reage a alteracoes remotas via onSync
- A cor final e derivada de _accountPrimaryColor ?? _localPrimaryColor, evitando corrida entre as preferencias locais e o sync
- Matrix notifica a troca de conta activa em initMatrix, setActiveClient e logout, corrigindo o indice do cliente activo
- Apagar o wallpaper preserva a cor; testes de serializacao do modelo

lib/utils/account_config.dart

@@ -27,20 +27,35 @@ extension ApplicationAccountConfigExtension on Client {
         wallpaperOpacity:
             config.wallpaperOpacity ?? currentConfig.wallpaperOpacity,
         wallpaperBlur: config.wallpaperBlur ?? currentConfig.wallpaperBlur,
+        primaryColor: config.primaryColor ?? currentConfig.primaryColor,
       ).toJson(),
     );
   }
+
+  Future<void> setApplicationAccountColor(int? primaryColor) {
+    final currentConfig = applicationAccountConfig;
+    return setApplicationAccountConfig(
+      ApplicationAccountConfig(
+        wallpaperUrl: currentConfig.wallpaperUrl,
+        wallpaperOpacity: currentConfig.wallpaperOpacity,
+        wallpaperBlur: currentConfig.wallpaperBlur,
+        primaryColor: primaryColor,
+      ),
+    );
+  }
 }
 
 class ApplicationAccountConfig {
   final Uri? wallpaperUrl;
   final double? wallpaperOpacity;
   final double? wallpaperBlur;
+  final int? primaryColor;
 
   const ApplicationAccountConfig({
     this.wallpaperUrl,
     this.wallpaperOpacity,
     this.wallpaperBlur,
+    this.primaryColor,
   });
 
   static double _sanitizedOpacity(double? opacity) {
@@ -58,11 +73,13 @@ class ApplicationAccountConfig {
           json.tryGet<double>('wallpaper_opacity'),
         ),
         wallpaperBlur: json.tryGet<double>('wallpaper_blur'),
+        primaryColor: json.tryGet<int>('primary_color'),
       );
 
   Map<String, dynamic> toJson() => {
     'wallpaper_url': wallpaperUrl?.toString(),
     'wallpaper_opacity': wallpaperOpacity,
     'wallpaper_blur': wallpaperBlur,
+    'primary_color': primaryColor,
   };
 }