Add instructor email notifications for pending requests

[alxstx]

Summary

• Add configurable email notifications for instructors when there are pending extension requests
• Instructors can choose daily or weekly digest frequency and specify a notification email in course settings
• Added PendingRequestsNotificationJob and rake task notifications:send_pending_digests[daily|weekly] for cron scheduling

Changes

• Added pending_notification_frequency and pending_notification_email columns to course_settings
• Added validations, normalization callbacks, and query scope to CourseSettings model
• Added PendingRequestsNotificationJob to send digest emails with pending request count and link
• Added pending notification params to CourseSettingsController permit list
• Added rake task for cron scheduling
• Added frequency dropdown and notification email field to General Settings tab
• Added Stimulus toggle to disable email field when no frequency is selected

Test plan

• Model validation and scope tests (spec/models/course_settings_spec.rb)
• Job tests (spec/jobs/pending_requests_notification_job_spec.rb)
• Controller tests (spec/controllers/course_settings_controller_spec.rb)
• Rake task tests (spec/tasks/notifications_rake_spec.rb)

Closes #344

🤖 Generated with Claude Code

[superconductor-for-github]

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[cycomachead]

This looks great!

I might have a couple more comments, but I think two things are worth addressing:

• there's a couple minor merge conflicts
• this doesn't do much until Make sync enrollments and sync assignments async with Good_job gem #379 is merged in
• Make sync enrollments and sync assignments async with Good_job gem #379 will probably create another small schema conflict.

So, I think you can merge main+379 into your branch. We should then figure out what the syntax is to have cron jobs.
I assume we essentially want 2 cron jobs scheduled in good job, one with the weekly argument, and a daily job with the daily argument?