feat: support quick switching between multiple Codex accounts / auth profiles

[Fanzzzd]

I’d like to request first-class support for switching between multiple Codex accounts / auth profiles from inside T3 Code.

Why

The main use case is quota management:

• one Codex account runs out of usage / rate-limit headroom
• I want to continue immediately with another account that still has quota
• I should not need to manually log out, rewrite config, or restart the whole app just to switch accounts

Secondary use cases:

• personal vs work account
• different auth profiles exposed by Codex CLI
• separate billing / quota pools for different tasks

Requested scope

• Detect or allow configuration of multiple Codex auth profiles / accounts
• Add an in-app account/profile switcher
• Clearly show which account/profile is currently active
• Make it easy to switch before starting a new session, and ideally during normal app usage
• Optionally surface quota/rate-limit state next to each account/profile if that data is available

Suggested acceptance criteria

• Users can see more than one available Codex account/profile.
• Users can switch to another account/profile without manually editing files or re-onboarding the app.
• New sessions use the selected account/profile predictably.
• The app clearly defines what happens to already-running threads after an account switch.
• If quota/rate-limit data is available, users can tell which account still has headroom before switching.

Relevant code context

• apps/web/src/appSettings.ts
• apps/web/src/routes/_chat.settings.tsx
• apps/server/src/codexAppServerManager.ts

Reference implementation ideas

• CodexMonitor already uses Codex argument/profile concepts and has richer account/config plumbing.
• A minimal first version could support switching between named Codex auth profiles (for example via Codex CLI profile args or separate auth homes), then expand into a fuller account manager later.