Fix#3453.
Thanks to #3499, #3500 and #3521, most of the obstacles to read-only installation have been resolved. This PR addresses the final piece, ensuring that SillyTavern no longer changes directories to `serverDirectory` and outputs files there. Instead, it outputs or copies necessary files to the directory where it is being run. Now, `serverDirectory` is read-only for SillyTavern (i.e., SillyTavern will not attempt to modify `serverDirectory`). Additionally, this PR sets the permissions for copied `default-user` files to be writable, so even if SillyTavern is installed as read-only, the copied `default-user` folder can still be modified.