fix: clean up previous test containers before starting new ones in CI

.github/workflows/ci.yml

@@ -163,6 +163,9 @@ jobs:
           docker build -t carbon-server:test .
       - name: Test Docker container startup
         run: |
+          # Clean up any previous test containers
+          docker rm -f carbon-test 2>/dev/null || true
+          
           # Start container in background
           docker run -d --name carbon-test -p 8080:8080 carbon-server:test
           # Wait for server to start (healthcheck needs time)