Fix running without launcher

[valpackett]

• mkdir ~/.local/config/openclaw to make the auto-generated config write succeed
• fix the auto-generated config
• use a CMake variable to specify the assets path for the auto-generated config
• create the default save in memory if it wasn't found on disk

[pjasicek]

First of all, sorry for not reviewing this pull request for such a long time.

Basically, at the moment, the OpenClaw in official release is meant to always be run through the launcher - it takes care of both selecting the proper saves and config file and makes it feasible to edit in-game options. Mainly editing the in-game options is a bit cumbersome without it - modifying XML for a non software-dev.

If ever I deem necessary to make it able to run without a launcher in official release, I will revisit this solution.

Thank you :)