feat: enforce canonical issue checkout contracts (#174)

[fujiwaranosai850]

Summary

• persist per-issue checkout contract state and expose checkout status in operator-facing project surfaces
• attach canonical checkout metadata during dispatch, render it in worker task messages, and preserve it across PR-feedback flows
• enforce checkout provenance and DevClaw branch/PR rules during worker completion, then align prompts and docs with the devclaw-local-dev vs devclaw-local-current model

Testing

• npm run build
• npm run check (currently fails in this workspace because vitest and some openclaw/plugin-sdk/* type modules are unresolved here)

Closes #174