SITE_ID_CURRENT_SITE vs BLOG_ID_CURRENT_SITE

This is a code consistency/standard thing.

SITE_ID_CURRENT_SITE vs BLOG_ID_CURRENT_SITE vs BLOGID_CURRENT_SITE

Why different options?

MySLP uses a lot of SITE_ID_CURRENT_SITE.
looks to be related to get_network_option() calls.

Some places use BLOG_ID_CURRENT_SITE.
Mostly, but not exclusively, for swith_to_blog() calls.

Both are defined in the Docker composer and both are set to 1.

Looks to be a legacy thing where there was (is?) a plan to have a network (the SITE ID) of blogs (the blog ID). In our case they will be one and the same.