[SIMPL-30451] Correct stale references in the guide and verify both images build

The rename of process_work_units and _results_from_pipes during the fan-out refactor left three references behind, in the guide, the checklist and the loosely coupled module docstring. The guide also showed loosely_coupled_k8s_job without its executor_def and claimed the pipes client replaced the executor, which stopped being true once the graph fanned out.

Both images were built and smoke tested: the code location image loads its definitions, and the payload image ships dagster_pipes without dagster. That check is now recorded as L11 in the readiness checklist, so the isolation argument is verified at image level and not only in the source.

Changelog: fixed

README.md

@@ -77,6 +77,10 @@ docker build -t distributed-execution:0.1.0 .
 docker build -f payload/Dockerfile -t distributed-execution-payload:0.1.0 payload/
 ```
 
+Both images build and have been smoke tested locally: the code location image
+loads its definitions, and the payload image contains `dagster_pipes` without
+`dagster` — check L11 in the readiness checklist.
+
 ## Status
 
 Both execution targets are implemented. The tightly coupled jobs and the loosely