* chore: add check-types
* refactor: api package file structure update
* feat: add headless worker extension API
* feat: add HeadlessCmd to manifest schema
* feat: make each type of cmds optional in manifest
There may be more types of cmds in the future, this makes backward compatibility easier.
* feat: implement headless extension command in app
A demo cmd implemented as well.
* refactor: move api package's API server files
* refactor: reformat all
