Implement rate limiting and enhance authentication flow

- Added rate limiting configuration for authentication endpoints, allowing customizable request limits via environment variables.
- Updated authentication flow to utilize HttpRequest for cookie management, ensuring secure handling of refresh tokens.
- Introduced a new endpoint to retrieve user subscription details.
- Enhanced the handling of Telegram bot token validation to prevent errors with empty tokens.
- Updated the application to serialize enums as strings for better documentation and compatibility with TypeScript.
- Improved test coverage for new features and adjustments in command handlers.

backend/src/PnvPanel.Infrastructure/DependencyInjection.cs

@@ -26,10 +26,12 @@ public static class DependencyInjection
 {
     public static IServiceCollection AddInfrastructure(this IServiceCollection services, IConfiguration configuration)
     {
-        var connectionString = configuration["ConnectionStrings:Default"]
-            ?? throw new InvalidOperationException("Строка подключения 'ConnectionStrings:Default' не сконфигурирована.");
-
-        services.AddDbContext<AppDbContext>(options => options.UseNpgsql(connectionString));
+        // Строка подключения читается лениво внутри лямбды (а не в локальную переменную сразу), иначе
+        // в тестах WebApplicationFactory.ConfigureAppConfiguration (Testcontainers-порт) не успевает
+        // примениться до регистрации DbContext — окажется закэширован дефолт из appsettings.json.
+        services.AddDbContext<AppDbContext>(options => options.UseNpgsql(
+            configuration["ConnectionStrings:Default"]
+                ?? throw new InvalidOperationException("Строка подключения 'ConnectionStrings:Default' не сконфигурирована.")));
         services.AddScoped<IAppDbContext>(sp => sp.GetRequiredService<AppDbContext>());
 
         services