Publish security and upstream guides as bilingual pairs

[novelKR]

Issue

Closes #

Summary

The security and implementation groups are now reviewed bilingual pairs: security-model, runner-isolation, error-codes, codex-reuse, upstream-lock, and upstream-update. Public titles no longer use W05 or W13. Overview links those pages. Gateway policy remains the only allow path. Codex stays a pinned implementation dependency, not an embedded agent. The site still does not deploy from this PR.

Contract changes

None. No MCP tool schemas, error codes, or status values change. This PR documents the existing codes.

Tests

Verified locally with Node 24.21.0 and Python 3.14:

python3.14 -B scripts/check_docs.py
npm run build --prefix docs-site
python3.14 -B docs-site/scripts/site.py check --commit "$(git rev-parse HEAD)"

site.py check --commit passed on a clean tree (139 hashed files, 33 HTML pages).

Security scenarios

• docs/workspaces.example.json and third_party/codex are not site pages. Prose links remap to GitHub blob URLs.
• Korean and English both record that exec_command is a host process today and that Linux container isolation is the target, not a verified laptop claim.
• Token redaction and CODESPACE_HTTP_TOKEN logging rules stay the same in both languages.

Out of scope

• Pages environment settings and live URL
• Publishing third_party/codex or docs/workspaces.example.json as site pages
• Changing the Codex pin or adding adapter crates

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