fix: Allow UpdateBotTokenAsync to start bot when not previously running

When TeleBot starts without a token configured, the TelegramBotService
returns early from StartAsync without creating a bot client. Previously,
UpdateBotTokenAsync only worked when _botClient was already initialized.

This fix changes the condition to also start the bot if _botClient is
null, enabling remote configuration via the discovery API to properly
start Telegram polling.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

TeleBot/TeleBot/TelegramBotService.cs

@@ -229,12 +229,16 @@ namespace TeleBot
 
         public async Task UpdateBotTokenAsync(string newToken)
         {
-            if (_botClient != null && _currentBotToken != newToken)
+            // If bot wasn't started or token changed, start/restart
+            if (_currentBotToken != newToken || _botClient == null)
             {
-                _logger.LogInformation("Updating bot token and restarting bot...");
+                _logger.LogInformation("Starting/updating bot with new token...");
 
-                // Stop current bot
-                _cancellationTokenSource?.Cancel();
+                // Stop current bot if running
+                if (_botClient != null)
+                {
+                    _cancellationTokenSource?.Cancel();
+                }
 
                 // Create new bot client with new token and TOR support
                 _currentBotToken = newToken;