feat: harden hiui-design planning and align workflow skill contracts

[1108guorui-web]

Summary

• harden hiui-design planner/runtime governance and legacy readiness handling
• align hiui-page-workflow with requiredActions-based planner contracts and explicit gate snapshots
• normalize refine-product-requirements handoff gates and tighten ux-walkthrough completion boundaries

Validation

• git diff --check
• skill_lint.py skills/hiui-page-workflow
• targeted contract and fixture checks for refine -> workflow -> hiui-design -> ux-walkthrough
• ux-walkthrough precheck_walkthrough.py smoke run

Notes

• ux-walkthrough docx completion now explicitly depends on python-docx in the runtime
• branch pushed from 1108guorui-web/hiui:feat/edit-hiui-design-skill-guorui20-0707