fix(codex): preserve official auth per instance

[MARYCOMPLEX]

Fixes #1240
Fixes #1802

Problem

Codex instances treated the login identity and API routing as one selection. Binding an account could replace the default OAuth identity and routing config, breaking setups that keep the official login while sending model requests through a third-party provider. The speed control was also missing from the official-login flow.

Solution

• Store the official OAuth account separately from the selected API provider for each instance.
• Project official credentials and provider routing together without replacing the instance identity.
• Reuse the account picker for both selections, including plan and quota details.
• Keep the speed selector available and make clearing the official account explicit across the Tauri command boundary.
• Add localized copy for the new flow.

Testing

• npm run build
• cargo check --manifest-path src-tauri/Cargo.toml
• cargo fmt --all -- --check

Demo

Watch the video

[MARYCOMPLEX]

@miso777 @Parcheal Could you give this a try and let me know if it works with your setup?