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/tests/PnvPanel.IntegrationTests/TestSupport/PnvPanelWebApplicationFactory.cs

@@ -27,7 +27,10 @@ public sealed class PnvPanelWebApplicationFactory : WebApplicationFactory<Progra
         .WithPassword("pnvpanel")
         .Build();
 
-    public async Task InitializeAsync() => await _postgres.StartAsync();
+    public async Task InitializeAsync()
+    {
+        await _postgres.StartAsync();
+    }
 
     async Task IAsyncLifetime.DisposeAsync()
     {
@@ -48,6 +51,9 @@ public sealed class PnvPanelWebApplicationFactory : WebApplicationFactory<Progra
                 ["AdminSeed:Password"] = AdminPassword,
                 // Пусто — TelegramBotHostedService при пустом токене не стартует (см. Api/Telegram/TelegramBotHostedService.cs).
                 ["Telegram:BotToken"] = "",
+                // Весь collection делит один TestServer/host — все запросы идут от одного "клиента",
+                // дефолтный лимит 20/мин быстро исчерпывается. Поднимаем для тестового окружения.
+                ["RateLimiting:AuthPermitLimit"] = "10000",
             });
         });