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/Auth/AuthFlowTests.cs

@@ -77,7 +77,7 @@ public class AuthFlowTests(PnvPanelWebApplicationFactory factory)
         var first = await client.PostJsonAsync("/api/auth/register", new { userName, password = "P@ssw0rd123" });
         Assert.Equal(HttpStatusCode.OK, first.StatusCode);
 
-        var second = await client.PostJsonAsync("/api/auth/register", new { userName, password = "AnotherPass123" });
+        var second = await client.PostJsonAsync("/api/auth/register", new { userName, password = "AnotherPass123!" });
 
         Assert.Equal(HttpStatusCode.Conflict, second.StatusCode);
     }