add support of active admin v4

[senid231]

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[Copilot]

Pull request overview

This PR adds support for ActiveAdmin v4 by introducing version-aware behavior (notably around the Devise login view override) and updating development/CI dependency stacks so the gem can be exercised against both the AA 3.5 and AA 4.0 lines.

Changes:

• Add an ActiveAdmin::Oidc.aa_v4? version probe and use it to select AA4-compatible Tailwind login markup.
• Split dependency stacks into per-version gemfiles and update CI to run specs against both stacks via BUNDLE_GEMFILE.
• Broaden the gemspec ActiveAdmin dependency to < 5 and adjust ancillary repo config (.gitignore, Gemfile).

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
lib/generators/active_admin/oidc/install/templates/sessions_new.v4.html.erb	New AA4-tailored login view template (Tailwind markup).
lib/generators/active_admin/oidc/install/install_generator.rb	Selects which login view template to publish based on AA version.
lib/activeadmin-oidc.rb	Introduces aa_v4? helper for AA version detection.
gemfiles/activeadmin_4.0.gemfile	Defines the AA4/Rails 8/Tailwind development stack.
gemfiles/activeadmin_3.5.gemfile	Defines the AA3.5/Rails 7.2/Sprockets development stack.
Gemfile	Defaults local development to the AA3.5 gemfile via eval_gemfile.
app/views/active_admin/devise/sessions/new.html.erb	Runtime AA3 vs AA4 branching for the login page markup.
activeadmin-oidc.gemspec	Expands ActiveAdmin dependency to < 5; moves asset-stack deps out of gemspec.
.gitignore	Ignores gemfile lockfiles and additional dummy app temp/log paths.
.github/workflows/ci.yml	Switches CI to a gemfile-based matrix (AA3.5 + AA4.0).

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