Improve Threadsmith operator comfort

[Teddy-creator]

Summary

• make Threadsmith full closeout human-first with a compact protocol footer
• add writeback tier file allowlist and closeout report opt-in rules
• add surfaceAudience/workVisibility recommendation metadata and routing tests
• add operatorExplanationStyle preference resolution
• document timestamp, command fallback, heartbeat evidence, and temporary artifact rules

Verification

• npm run verify:skill-contract
• npm run test --workspace @threadsmith/domain
• npm run test --workspace @threadsmith/runtime
• npm run test --workspace @threadsmith/orchestrator
• npm run verify:project-truth
• git diff --check

No release work. Global skill sync should happen only after merge.