[FEATURE]: Multi-project core and API #13623

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

The current API does not expose a POST endpoint to change the active project. Even after switching projects in the desktop app, /project/current still returns the previous project. I’d like to run a single opencode instance/server and be able to interact with multiple projects via the API, and also changing the active project from the TUI.

So, instead of having a current project, there should be just projects. Then API can interact with all projects and TUI is attached to a single project, being able to change to another