Update dependencies and refactor ActiveAdmin filters for clarity

[rsmoke]

This pull request focuses on improving the admin interface and search functionality for applications and users, mainly by correcting UI labels and enhancing how the conf_year attribute is handled in Ransack searches to avoid ambiguity. Additionally, it includes a minor fix to a database query and updates related tests.

Admin UI improvements:

• Corrected the spelling of the "User Management" menu label in both app/admin/applications.rb and app/admin/users.rb for consistency and professionalism.
• Updated the filter for conference year in the applications admin page to use a disambiguated label and attribute (applications_conf_year), making it clearer and preventing conflicts when joining associated tables.

Search and filtering enhancements:

• Added a new Ransack ransacker applications_conf_year to the Application model to disambiguate the conf_year field in complex searches, and included it in the list of ransackable attributes.
• Updated the related RSpec test to include applications_conf_year in the expected ransackable attributes, ensuring test coverage for this change.

Code quality and query improvements:

• Refactored the current_conference_payments scope in the Payment model to use Arel for better query safety and clarity.