fix: add Email related db components to diagram and db-admin dashboard

[amandazhuyilan]

Description

Update the DB diagram and db admin dashboard with missing email related components.

Changes

• Added the missing Email related models to the diagram generator so they appear in the output.
• Added EmailNotification admin view and wired it up so notifications show in the dashboard.

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 to me