Add OpenAI generation provider

[moose-lab]

Summary

• add direct OpenAI provider support for /api/generations via Responses and Images APIs
• add chatgpt-oauth as the default generation provider for the Hero workflow and backend omitted-provider path
• forward ChatGPT Action Authorization bearer tokens into repo analysis, launch planning, and image generation without persisting token values
• document required server env vars, including CHATGPT_OAUTH_ACCESS_TOKEN for local/dev fallback, while keeping Wavespeed/mock compatibility

Test Plan

• npm test -- --run api/generations.test.ts src/server/generation/generation.test.ts src/App.test.tsx
• npm test
• npm run build
• git diff --check

Notes

chatgpt-oauth expects a ChatGPT Action-style Authorization bearer token on the request or CHATGPT_OAUTH_ACCESS_TOKEN in server runtime configuration. Model call metadata records only credentialSource, not token values.