[SIMPL-30787] Document container-cluster configuration inputs

Add the cluster-configuration input reference the guide was missing: which inputs are mandatory, conditional or optional in each setup, a reusable minimum input set, and worked examples expressed in the format each setup already uses. No configuration schema or key naming is prescribed.

Retitle the subject sections so they no longer carry one story's AC numbering, and add a traceability section mapping SIMPL-30787 and SIMPL-30451 acceptance criteria onto them.

Changelog: added

documents/user-guide/readiness-checklist.md

@@ -1,7 +1,10 @@
 # Distributed Execution: Readiness Checklist
 
 Pre-run validation for a workflow's execution target. Companion to the
-[user guide](distributed-execution-guide.md); this document covers AC3.
+[user guide](distributed-execution-guide.md); this document is the validation
+checklist required by SIMPL-30451 AC3 and SIMPL-30787 AC3. Section 1 holds the
+checks common to both setups, section 2 the tightly coupled checks and section 3
+the loosely coupled ones; every item states the evidence that proves it.
 
 Run these checks **before the first execution** of a workflow, and again after any
 change to the run launcher, the executor, the target namespace or the code