Plugin: add CI and release publish workflow

[huntharo]

Summary

• add GitHub Actions CI and tag-driven publish workflows following the ghcrawl pattern
• add release helper scripts and the repo-local .agents/skills/release skill
• switch the package to the unscoped openclaw-codex-app-server name, pin 0.0.0, and tighten published package contents

Validation

• pnpm typecheck
• pnpm test
• pnpm pack:smoke
• python3 -m py_compile .agents/skills/release/scripts/release_plan.py

Notes

• GitHub Actions publish workflow expects the NPM_TOKEN secret
• OVERNIGHT-TODO.md is intentionally left out of this PR