fix(tests): mark demo_docker_executor as #[ignore] Refs #2733

Test requires Docker daemon and python:3.11-slim image to be present.
Without those prerequisites the test panics unconditionally, breaking
`cargo test --workspace` on standard CI runners. Mark it ignored so it
is skipped by default and can be run explicitly with `--ignored` when
the environment is ready.

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

Author: Test User

crates/terraphim_rlm/tests/backend_demo.rs

@@ -52,6 +52,7 @@ async fn demo_local_executor() {
 }
 
 #[tokio::test]
+#[ignore = "requires Docker daemon with python:3.11-slim image; run with --ignored to enable"]
 async fn demo_docker_executor() {
     println!("\n═══════════════════════════════════════════");
     println!("  DOCKER EXECUTOR (container isolation)");