Update dependencies and drop obsolete json pin

[tagliala]

Summary

Updates the lockfiles and removes the now-obsolete json < 3.0 pin.

This update was produced automatically by AI.

Dependency updates

• bundler 4.0.21 → 4.0.22
• rails / activesupport / actionpack / etc. 8.1.3.1 → 8.1.4
• net-smtp 0.5.1 → 0.5.2
• rdoc 8.0.0 → 8.1.0
• regexp_parser 2.12.0 → 2.13.1
• unicode-display_width 3.2.0 → 3.3.0
• unicode-emoji 4.2.0 → 4.3.0

All of these were verified to support Ruby >= 3.2, which is this gem's
required_ruby_version floor and the lowest Ruby in the CI matrix. The
lockfiles were regenerated on Ruby 3.2.11 to keep them valid for every
supported Ruby version.

Dropping the json pin

The previous run pinned json < 3.0 because Rails 8.1 passed a positional
options hash to JSON.parse from ActiveSupport::JSON.decode, which json
3.0 rejects (rails/rails#58601).

That fix shipped in Rails 8.1.4, so the pin and its matching dependabot
ignore rule are no longer needed. json now resolves to 3.0.2.

The pin only ever existed in the root Gemfile (which targets Rails 8.1);
the gemfiles/* Gemfiles never declared json and are unaffected.

Test plan

• bundle exec rspec — 140 examples, 0 failures
• bundle exec rubocop — 57 files inspected, no offenses detected

Full CI matrix (Ruby 3.2–4.0 × Rails 7.0–8.1) will run on this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.33%. Comparing base (3e294d1) to head (601c405).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #745   +/-   ##
=======================================
  Coverage   94.33%   94.33%           
=======================================
  Files          17       17           
  Lines         459      459           
=======================================
  Hits          433      433           
  Misses         26       26           

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