Clean up remaining Sequelize dependencies

[TooAngel]

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