docs: Standardize naming: use "GRASS" instead of "GRASS GIS"

[lindakarlovska]

This pull request updates the terminology in documentation files by replacing "GRASS GIS" with the simplified form "GRASS", in line with current naming conventions used in the project.

Changes were made in the following paths:

• grass/gui/wxpython/docs
• grass/lib/init
• grass/doc

Exclusions:

• Files under grass/doc/development/rfc/ remain unchanged (they reflect the terminology as it was at the time they were written).
• The file grass/lib/init/grass.py was intentionally left out, as it is not part of the documentation. It will be addressed in a separate pull request.

The replacement was applied to:

• lines where "GRASS GIS" appeared in a single line, located using:
  grep -Irni "GRASS GIS"

• and cases where "GRASS" appeared on one line and "GIS" on the next line, located using:
  pcregrep -M 'GRASS\s*\n\s*GIS' $(find . -name '*.md')

[veroandreo]

I fixed one sentence that didn't read well and added the GRASS tutorials repo that was missing.

[lindakarlovska]

I fixed one sentence that didn't read well and added the GRASS tutorials repo that was missing.

Thanks Vero!