Author personas and journey flows

For: Spec Author

Part of: gen-user-docs

Steps

• Add (spec): personas[] to system.usm (id, name, description)
• Annotate (spec): flows with actor (flow-level or per-step) and optional surface, marking them as journeys
• The system validate: schema: persona ids referenced by actor exist; unknown actors rejected (hard error in generate pass)
• Review (browser): composed user docs rendered live via usm docs serve