[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

src/distributed_execution/loosely_coupled/jobs.py

@@ -6,7 +6,7 @@ dagster-pipes protocol, which Dagster materialises as logs and metadata. The
 payload never connects to the metadata database.
 
 Two transports are provided. Both dispatch the *same* payload script and produce
-the same output shape as the tightly coupled ``process_work_units`` op, so the
+the same output shape as the tightly coupled ``process_work_unit`` op, so the
 graphs differ by exactly one node - see the guide's section 5.3.
 """