[codex] Add configurable OpenAI-compatible gateway

[Neonity2020]

What Changed

Why

UI Changes

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Summary

Adds a PeakCode-hosted OpenAI-compatible gateway so Codex can route selected
third-party models through the app instead of requiring each tool to be
configured independently.

What changed

• Added gateway contracts, RPC plumbing, server service wiring, and settings
  UI for configuring upstream providers and API keys.
• Added DeepSeek V4 Flash/Pro defaults and alias handling for legacy DeepSeek
  model names.
• Routed Codex DeepSeek model selections through a local peakcode-gateway
  Codex provider overlay.
• Added OpenAI-compatible /models, /chat/completions, and /responses
  gateway endpoints, including Responses-to-Chat translation for Codex.
• Cleaned up stale Codex overlay provider config so switching back from
  DeepSeek gateway models to GPT-5.5 restores the normal Codex provider path.

Validation

• vitest run src/http.test.ts --testTimeout=10000
• vitest run src/codexAppServerManager.test.ts --testTimeout=10000
• git diff --check
• npm run dist:desktop:dmg:arm64

Notes

Full workspace bun fmt, bun lint, and bun typecheck were not run in this
session per local AGENTS.md guidance unless explicitly requested.

[jwangkun]

感谢这个 PR 付出的工作 @Neonity2020 👍

很遗憾这个 PR 我们没法合并,主要原因如下:

与现有的 gateway 实现严重冲突。 最近 main 上已经合入了一套 model channel gateway 方案(见 commit e743f72),覆盖了几乎相同的文件集:

• packages/contracts/src/gateway.ts —— 双方都新增(add/add 冲突),但是两套完全不同的设计:
  • 本 PR: GatewayUpstreamConfig + GatewayFallbackStrategy(retry/skip/fail)+ 模型动态发现,偏通用抽象。
  • 已合入方案: GatewayChannelConfig(openai/mimo/anthropic)+ 预设渠道 + API key 管理 + Codex overlay 注入,偏具体落地。
• apps/server/src/http.ts、codexProcessEnv.ts、codexAppServerManager.ts、_chat.settings.tsx、contracts(ipc/rpc/ws)均有内容冲突,共 9 个文件。

两套方案在职责上高度重叠,合并意味着推倒重来,因此只能二选一。目前仓库已经采用了落地版本,所以先关闭这个 PR。

如果后续有部分能力(例如 fallback 策略、模型动态发现)想作为补充合进来,欢迎基于最新的 main 重新开一个聚焦的小 PR,避免和现有 gateway 模块冲突。再次感谢贡献 🙏