ci: replace Thor releases with Release Please and trusted publishing

[KazuCocoa]

Replace appium_thor release tasks with Release Please and RubyGems Trusted Publishing, following appium/ruby_lib_core#704. Maintainers review and merge a release PR; version, date, changelog, tag, GitHub Release, and publication are automated.

• Use the built-in GITHUB_TOKEN and explicit workflow dispatch; no custom GitHub App or PAT.
• Bootstrap from 4.2.0 and preserve historical release notes.
• Use the shared ruby-release-validate action from feat: add shared Ruby release validation action appium-workflows#12, pinned to its merged commit, for PR and tagged-package validation. No duplicated helper or helper tests remain here.
• Upload the verified artifact and pass its filename to the publishing job, which downloads into its own pkg/ directory and authenticates using OIDC.
• Retain runtime thor and arc. Fix the obsolete RuboCop cop name so lint can run. The old thor spec task referred to a nonexistent spec directory.
• Document initial setup, explicit versions, RCs, local shared-validator usage, and recovery.

Validation

Local gem build, shared action validation on the built artifact, simulated artifact filename transfer between jobs, actionlint, and whitespace checks passed. The shared validator has passing Ruby 3.1/3.4/4.0 tests in its own repository. The initial migration also passed local library/lint or CLI smoke checks, as applicable. No gem was published or remote publication settings changed.

Activation

Allow Actions to create PRs, create the rubygems GitHub environment, and register a Trusted Publisher on appium_console with owner appium, repository ruby_console, workflow publish-gem.yml, and environment rubygems. The shared composite action does not change this registration. See RELEASING.md for required checks and limitations of event-only PR checks.

Together with the other Ruby migrations, this removes release dependencies on appium_thor so it can subsequently be deprecated.