UAPF-specification v2.1.0 (SEM-011) makes cornerstone diagram interchange
mandatory. This CMMN file was hand-authored as logic only, with no
<cmmndi:CMMNDI>, so it did not render in any CMMN viewer.
Adds a complete CMMNDI: a nested layout of 20 shapes -- 1 case plan model,
4 stages, 11 plan items, 3 milestones, 1 entry criterion -- with child
bounds geometrically contained within their parents. The case model logic
is byte-identical; only diagram interchange was added.
