Make ceremony output recovery atomic

[mellowcroc]

Summary

• make identity generation and ceremony initialization safe to resume after interruption
• publish native finalization artifacts through the existing fresh staging directory without Docker Desktop-incompatible per-file hard links
• return structured command outcomes for Relay recovery decisions
• add regression coverage and updated CLI guidance

Validation

• complete Linux/ARM64 Docker rehearsal passed: 3+3 contributions, two real beacon rounds, finalization, audits, operational evidence, release signing and verification
• Relay all-role interactive Docker onboarding passed
• macOS package tests reach known platform-only symlink and Linux executable-identity constraints; CI provides the authoritative Linux run