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.Application.Tests/Auth/GetCurrentUserQueryHandlerTests.cs

@@ -40,7 +40,7 @@ public class GetCurrentUserQueryHandlerTests
     public async Task Handle_AuthenticatedWithProfile_ReturnsCurrentUserDto()
     {
         var userId = Guid.NewGuid();
-        var profile = new CurrentUserProfile(userId, "alice", Guid.NewGuid(), "user", true, false, 3);
+        var profile = new CurrentUserProfile(userId, "alice", Guid.NewGuid(), "user", true, false, 3, "sub-token");
         _identityService.GetProfileAsync(userId, Arg.Any<CancellationToken>()).Returns(profile);
         _identityService.GetTelegramLinkInfoAsync(userId, Arg.Any<CancellationToken>())
             .Returns(new TelegramLinkInfo(true, 42, "alice_tg"));