fix: preserve preset persona for team members

[lisihao]

Summary

• add configurable memberPersonaPlacement with backward-compatible system default
• allow prompt placement to keep the child preset deployment persona unchanged
• persist the full member protocol in the initial user message for prompt mode
• add regression coverage for providers without scoped persona support
• document Anchored Standard and other trajectory-sensitive preset usage

Verification

• pnpm verify
• pnpm build
• pnpm typecheck
• live DSH parent/worker Trace: identical Anchored Standard first system persona and bash + str_replace_editor bootstrap tools