Adds scripts/smoke_check.sh: installs the freshly-built .gem into a
sandbox GEM_HOME and runs `ruby -rquonfig -e 'puts Quonfig::VERSION'`.
Wires it into both the Rakefile :release task and the release.yml
workflow, gated between `gem build` and `gem push`. Aborts the publish
if `require 'quonfig'` raises or the loaded VERSION mismatches.

Prevention measure for qfg-e588: 0.0.9 shipped with a stale gemspec
manifest missing lib/quonfig/evaluation_details.rb. Every consumer hit
LoadError at install time. The 0.0.10 gemspec already lists the file
(regenerated 2026-05-01); this commit makes sure a future regression
can never reach RubyGems silently again.

Closes qfg-e588 (paired with the QUONFIG_DOMAIN work in 60951f2 that
closes qfg-w6gg).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>