The `AnA` linter should allow both "a SNES" and "an SNES"

I always pronounced that console as "ess en ee ess" OR "Super Nintendo" and didn't hear it pronounced as an acronym until recent years on YouTube.

Ideally it should be a user pref but I think other terms that accept both do not have any kind of pref either.

Start by locating the AnA linter and its existing handling for terms that accept multiple articles. Add coverage for both “a SNES” and “an SNES,” then verify the linter accepts both forms without changing other article checks.

Written by the indexing model from the issue text.