Clean up remaining Sequelize dependencies

Remove remaining Sequelize models, configurations, and dependencies after MongoDB migration.

Context:

• Migration from SQL to MongoDB is complete
• Sequelize artifacts still remain in codebase
• Need cleanup for maintainability and reduced bundle size

Acceptance Criteria:

• Identify all remaining Sequelize files and configurations
• Remove Sequelize from package.json dependencies
• Clean up any Sequelize model files
• Remove Sequelize configuration files
• Test application functionality after cleanup

Priority: Medium

Start by searching the repository for remaining Sequelize models, configuration files, and dependency references, then inspect package.json. Remove the identified Sequelize artifacts and verify that application functionality still works after the cleanup.