feat: add Codex Provider Guard script

[k9ight000]

Summary

• add a Provider Guard marketplace panel
• show current/stable provider, indexed thread count, endpoint type, and provider bucket findings
• detect a sudden in-page thread count drop
• open the native Codex++ manager for confirmed repair

Security

• no arbitrary network requests
• no local storage or credential access
• no HTML injection sinks or dynamic code execution
• calls only the read-only /provider-guard/status\ bridge route and /manager/open`n- script SHA-256 matches the marketplace manifest

Requires the Provider Guard backend introduced by the companion CodexPlusPlus PR.