As a developer, I want to refactor Fertiscan's database schema to simplify its structure

[k-allagbe]

Description

After moving Fertiscan's datastore logic into fertiscan-backend, the database schema should be reviewed and refactored to remove unnecessary complexity.

Acceptance Criteria

• Database schema is simplified without breaking existing functionality.
• Models are updated to match the new schema.
• Migrations are generated to apply the schema changes.
• Fertiscan-backend continues to run correctly with the updated schema.