UAPF-specification v2.1.0 makes cornerstone diagram interchange mandatory
(SEM-011). This file was hand-authored as logic only. Adds the bpmndi/dc/di
namespaces and a complete BPMNDiagram (5 shapes, 4 edges, deterministic
linear layout). The <bpmn:process> logic is byte-identical.
UAPF-specification v2.0.0 mandates OMG-standard cornerstone extensions.
Renamed cornerstone files and updated references in README / docs /
processgit.mcp.yaml. Content of the BPMN/DMN files is unchanged.
