Improve workflow execution contracts and context efficiency

[shinpr]

Summary

• reduce generic coding and testing prompt surface while preserving repository, contract, boundary, and proof rules
• scope React and TypeScript references to web frontend work instead of backend or non-web TypeScript
• add explicit update_plan execution gates, terminal plan handling, blocked-state routing, and deterministic agent handoffs
• strengthen integration and E2E test review with executor write sets, changed-test derivation, skeleton context, proof obligations, and explicit RED applicability
• rewrite the README around workflow outcomes, recipe selection, inspectable handoffs, and progressive disclosure
• bump the package version to 0.9.3

Why

The previous prompts carried broad general knowledge but left several workflow transitions and handoff fields implicit. This change removes low-value prompt surface and makes the remaining execution contracts observable so recipes can complete without guessing, silently skipping a step, or losing modified tests between agents.

The README now explains when the additional workflow cost is worthwhile, when direct Codex execution is preferable, and how approved decisions remain traceable through implementation and review. It does not claim an unverified real-world run.

Validation

• npm test
• npm run check:skills-index
• git diff --check