Expand user search fields

[jvendetti]

Summary

• Preserve existing /users?search= behavior: default search remains username-only for backward compatibility.
• Add optional search_fields param so clients can opt into searching specific fields: username, email, firstName, and/or lastName.
• Add search_fields=all shorthand for searching all supported user search fields.
• Reject mixed all values such as search_fields=all,email; all must be used by itself.
• Add users controller tests for the username-only default, opt-in broad search, strict all handling, and no-match pagination metadata.
• Skip Minitest::Reporters when tests are launched from RubyMine so IDE test runs can use RubyMine's reporter.
• Fix some RuboCop warnings

Notes

BioPortal Admin Users can pass search_fields=all to search across all user table fields. Existing clients, including remote account pickers that expect username-only matching, can omit search_fields.

Verification

• ruby -c helpers/users_helper.rb
• ruby -c test/controllers/test_users_controller.rb
• bundle exec ruby test/controllers/test_users_controller.rb

Closes #225