v3.2.1 mermaid-first workflows

Greenfield, brownfield, and Spring Boot mapping now default C4, sequence, class, ER, state, and component diagrams to design-doc-mermaid.

PlantUML is leftover types only (Salt wireframes, use case, timing, ArchiMate, nwdiag, WBS) and always PNG or SVG.

GitHub wiki keeps fenced mermaid. Confluence needs images for both.

STE100 remains the default voice pack. Google style is exclusive opt-in. No em dash. No sentence starting with So, That, Thus, or Hence.