FIX: Update database schema, Sequelize models

Acceptance Criteria

• Update Sequelize models to reflect updated ER diagram following team meeting
• Update PostgreSQL setup scripts to match updated database schema.
• Update all affected app functionality to work with the updated models and test for/fix bugs arising from the refactor.

Definition of Ready

• Understood by the team
• Has clear business value
• Is estimated
• Has its dependencies linked
• Is small
• Has its acceptance criteria defined

Definition of Done

• Built and runs without errors
• Is tested against acceptance criteria
• Demoed to the team
• Documented and commented code
• Pages have some basic styling (if appropriate)
• Has at least 70% code coverage for automated testing
• Uses Selenium to full stack test (if appropriate)
• Has no ESLint errors