fix: Add snake_case JSON deserialization for Telegram API response

The Telegram API returns JSON with snake_case properties (first_name, is_bot)
but the DTOs use PascalCase. Added JsonSerializerOptions with
PropertyNameCaseInsensitive and SnakeCaseLower naming policy.

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

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

TeleBot/TeleBot/Services/BotManagerService.cs

@@ -567,7 +567,12 @@ public class BotManagerService : IHostedService, IDisposable
             if (response.IsSuccessStatusCode)
             {
                 var responseJson = await response.Content.ReadAsStringAsync();
-                var result = JsonSerializer.Deserialize<TelegramGetMeResponse>(responseJson);
+                var options = new JsonSerializerOptions
+                {
+                    PropertyNameCaseInsensitive = true,
+                    PropertyNamingPolicy = JsonNamingPolicy.SnakeCaseLower
+                };
+                var result = JsonSerializer.Deserialize<TelegramGetMeResponse>(responseJson, options);
                 return result?.Result;
             }
             else