AAI-461: send bundle approval emails when request is approved

[amandazhuyilan]

Description

AAI-461: send bundle approval emails to users when request is approved by bundle admins

Changes

• Added delivery plumbing so every group approval calculates whether the status actually changed before queueing an email
  • the FastAPI admin endpoint now injects BackgroundTasks, Settings, and EmailService, returns the updated membership from _approve_group_membership, and only schedules send_group_membership_approved_email when send_email is enabled and the user has just transitioned to approved
• Extended the BioCommons group approval route to share the same behavior and introduced a reusable send_group_membership_approved_email helper that builds the user-facing email with the bundle name and portal link so both admin and self-service approvals notify the user consistently
• Updated related tests

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have added unit / integration tests that prove my fix is effective or that my feature works
• I have run all tests locally and they pass
• I have updated the documentation (if applicable)
• For any new secrets, I have updated the shared spreadsheet and the GitHub Secrets.

[marius-mather]

Looks good, just a couple of nitpicks with the code

[marius-mather]

good to go