Implement preferred audio languages feature: update site settings to include preferred audio languages, modify related data structures and API endpoints, and enhance media processing to select audio tracks based on user preferences. Update frontend components for managing and displaying these settings.

backend/src/TeleWave.Infrastructure/Settings/SiteSettings.cs

@@ -14,13 +14,23 @@ public sealed class SiteSettings(IAppDbContext dbContext) : ISiteSettings
 
     public async Task SetRegistrationEnabledAsync(bool enabled, CancellationToken cancellationToken)
     {
-        var value = enabled ? "true" : "false";
+        await UpsertAsync(SettingKeys.RegistrationEnabled, enabled ? "true" : "false", cancellationToken);
+    }
+
+    public Task<string> GetPreferredAudioLanguagesAsync(CancellationToken cancellationToken) =>
+        dbContext.GetStringSettingAsync(SettingKeys.PreferredAudioLanguages, "", cancellationToken);
+
+    public Task SetPreferredAudioLanguagesAsync(string value, CancellationToken cancellationToken) =>
+        UpsertAsync(SettingKeys.PreferredAudioLanguages, value, cancellationToken);
+
+    private async Task UpsertAsync(string key, string value, CancellationToken cancellationToken)
+    {
         var existing = await dbContext.AppSettings.FirstOrDefaultAsync(
-            s => s.Key == SettingKeys.RegistrationEnabled,
+            s => s.Key == key,
             cancellationToken
         );
         if (existing is null)
-            dbContext.AppSettings.Add(AppSetting.Create(SettingKeys.RegistrationEnabled, value));
+            dbContext.AppSettings.Add(AppSetting.Create(key, value));
         else
             existing.SetValue(value);
     }