Add semester filter to Import Courses page

[alxstx]

Changes

• Added semester filter dropdown to the Import Courses page to filter courses by Canvas term
• Added filter_by_semester method to CoursesController to filter Canvas API course data by term name
• Updated course table to display semester from Canvas term data instead of creation date
• Collects unique semester names from Canvas API response for the filter dropdown

Testing

• Run bundle exec rspec spec/controllers/courses_controller_spec.rb for semester filter tests
• Run the full rspec test suite to verify no regressions

Documentation

No documentation needed

Checklist

• Name of branch corresponds to story
• 80%+ test coverage with all tests passing