fix: resolve TypeScript lint error in Docker entrypoint tests

- Add type guard to safely check for 'failed' property existence
- Use 'in' operator to handle union type properly
- Fixes TS2339 error: Property 'failed' does not exist on type

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

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

tests/integration/docker/docker-entrypoint.test.ts

@@ -582,7 +582,7 @@ describeDocker('Docker Entrypoint Script', () => {
           console.log(`Container ${i}:`, { 
             stdout: result.stdout, 
             stderr: result.stderr,
-            failed: result.failed 
+            failed: 'failed' in result ? result.failed : false
           });
         });
       }