fix: sync Codex skills through Agents roots

[freshtechbro]

Summary

• Coalesce Codex-managed OpenDevBrowser skill installs through the shared Agents roots to avoid duplicate opendevbrowser-* discovery entries.
• Refresh managed stale canonical packs while preserving unmanaged markerless skill directories.
• Add isolated Codex discovery, stale duplicate repair, and CODEX_HOME=$HOME/.agents alias regression coverage.
• Align README, CLI docs, AGENTS guidance, and best-practices skill wording with the new install/update lifecycle.

Tests

• ./skills/opendevbrowser-best-practices/scripts/validate-skill-assets.sh
• node scripts/docs-drift-check.mjs
• npm run typecheck
• npm run lint
• npm run build
• npm run test
• npm run extension:build
• npm run version:check
• git diff --check

Review Notes

• RepoPrompt final code review returned no findings.
• QA re-review confirmed final local quality-gate evidence resolves the prior evidence blocker.
• ULW C001, C002, and C003 are passed; final ULW completion checkpoint will run after PR checks/merge closeout.