Add human-centered governance mode

[Teddy-creator]

Summary

• add human-centered operating modes and writeback tiers
• add runtime recommendation metadata and unsafe legacy fallback
• add configurable value heartbeat preferences
• add human-centered output regression fixtures
• add docs hygiene inventory and closeout report

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 will happen only after merge.