Demo only: show the solargraph-rails Array#sum fix in plugin CI

[apiology]

Claude:

Do not merge

This branch exists only to produce CI logs. It pins solargraph-rails to a branch in a third-party repository (iftheshoefritz/solargraph-rails @ drop-array-sum-annotation), which will be deleted once iftheshoefritz/solargraph-rails#211 merges — at which point every job here breaks. Close it once the logs have been read.

What it demonstrates

iftheshoefritz/solargraph-rails#211 deletes def sum; end from the plugin's lib/solargraph/rails/annotations/array.rb. That stub contributes an arity-0, blockless () -> untyped overload to the combined Array#sum pin, alongside core rbs's (?untyped init) ?{ (E e) -> untyped } -> untyped. When the blockless overload wins, the block parameter in key_types.sum { |t| t.items.length } loses its element type.

Expected outcome

The rails and regression jobs should drop from 4 problems to 2, losing both of:

lib/solargraph/complex_type/type_methods.rb:219: Unresolved call to items
lib/solargraph/complex_type/type_methods.rb:219: Unresolved call to items

and keeping both Unneeded @sg-ignore comment results.

Note on the diff

The rails and regression jobs install solargraph-rails from RubyGems via .Gemfile, not from the git clone in run_solargraph_rails_specs. Changing only the clone target would have left those two jobs on the released gem, so the two .Gemfile lines are pinned to the branch as well. The clone target is changed too, so run_solargraph_rails_specs exercises the same branch.

This PR was written by Claude Code on behalf of @apiology.