Improve release-yield confirmation flow

[bigboateng]

Summary

• expose dry-run-only versus release mode before GitHub work
• require explicit confirmation for minor and major intent
• keep exact-version authorization before live publication
• simplify the canonical skill root by moving implementation and tests under src
• regenerate Codex, Claude Code, and Cursor adapters

Verification

• npm run test:selfhost (14 passed)
• npm run test:release (40 passed)
• npm exec --offline -- yskill doctor skills/release-yield --root . --agent codex,cursor,claude-code
• local CLI interaction verified dry-run -> minor -> confirmation -> cancel without GitHub activity