OpenHands

Fix SaaS routes shadowed by frontend mount
<https://github.com/OpenHands/OpenHands/pull/14279>
This is breaking feature deployment (cc <@U07EZMGJFBJ> <@U093U7MJ44B>)

Likely regression source: `5232d96dab0ca98e691d6307bd0759e943220d1c` (`refactor: Move openhands.server content to openhands.app_server`, <https://github.com/OpenHands/OpenHands/pull/14254|#14254>).
Why: before that commit, `<http://openhands.server.app|openhands.server.app>` only built the FastAPI app; the frontend `/` mount happened in `openhands.server.listen`. SaaS imported `<http://openhands.server.app|openhands.server.app>`, registered enterprise routes, and then mounted the frontend last. In `5232d96d`, the frontend mount moved into `<http://openhands.app_server.app|openhands.app_server.app>`, which SaaS imports before registering `/oauth/...`, so a built frontend can shadow later SaaS routes.

Hello <@U06QJHRBLQG>, I have approved the pull request. Thank you very much! :thankyou: