Add root route so GET / returns API info instead of 404

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app.ts

@@ -61,6 +61,7 @@ export async function buildApp(): Promise<FastifyInstance> {
 
   // Health check
   app.get('/health', async () => ({ status: 'ok', timestamp: new Date().toISOString() }));
+  app.get('/', async () => ({ name: 'Swiss System Tournament API', version: '1.0.0', docs: '/api/v1' }));
 
   // API routes
   await app.register(authRoutes, { prefix: `${API_PREFIX}/auth` });