fix(leaderboard-service): change global prefix from 'api' to 'api/v1'

Match the global prefix convention used by all other services.
This fixes Kong routing 404 errors for /api/v1/leaderboard/* endpoints.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/leaderboard-service/src/main.ts

@@ -25,7 +25,7 @@ async function bootstrap() {
   });
 
   // API 前缀
-  app.setGlobalPrefix('api');
+  app.setGlobalPrefix('api/v1');
 
   // Swagger 文档配置
   const config = new DocumentBuilder()