syscfg 20260619

NEWS:
* Fixed syscfg polluting the positional parameters of clients and files
  specified by $source. They will now have only $0 to access and all other
  parameters will be free to use, as was intended.
  Breaking (backward-incompatible) change.

* Fixed syscfg polluting the environment of clients and files specified by
  $source with readonly variables. From our point of view, clients and $source
  files will now have a mostly identical environment. Additionally clarified
  the environment for clients and $source files in documentation.

- Filtered log of core changes:
3153a53 syscfg: Fix pollution of client environment
7660e94 syscfg: Fix `.` positional parameters pollution

- Complete log between 20260617 and 20260619:
40ed640 syscfg 20260619
3153a53 syscfg: Fix pollution of client environment
7660e94 syscfg: Fix `.` positional parameters pollution