Upgrade repository trust surface and bilingual docs

[ToussaintKnight]

Summary

Upgrade Codex Sync2 from a technically solid private repository into a release-ready trust surface for agentic engineering.

What changed

• Reframed the README around the multi-device Codex pain, target user, executable proof, and ecosystem position.
• Moved the detailed privacy warning below Quick Start and retained a concise security note.
• Added paired English/Simplified Chinese README, security, contributing, changelog, demo, roadmap, and architecture documents with relative language switchers.
• Added an architecture diagram explaining the boundary between transport and Codex-semantic safety.
• Added privacy:scan to reject secrets, private paths, device IDs, private-network IPs, forbidden local-state files, and non-example email addresses.
• Added docs:check to validate local links, language switchers, heading parity, and fenced-code parity.
• Updated CI to run the full npm run check gate on Windows, macOS, and Linux.
• Updated actions/checkout and actions/setup-node to their current Node 24-based major versions.

Why

The repository already had strong implementation and tests, but its first screen led with risk instead of user value, public-facing documentation was English-only, CI had runtime deprecation warnings, and privacy checks were manual rather than reproducible.

Validation

• npm run privacy:scan — 35 files passed
• npm run docs:check — 19 Markdown files and 7 language pairs passed
• npm test — 65 checks passed
• git diff --check
• Git author uses the GitHub noreply address

Remaining boundary

The repository remains Private. This improves credibility and launch readiness, but it does not create public GitHub influence until visibility is explicitly changed and a real community launch is authorized.