Add Sequelize Database Client

[bbopar]

Is your feature request related to a problem? Please describe.
The current database implementation uses raw SQL queries which can be cumbersome to maintain and test. Adding a Sequelize client option would provide developers with a more familiar and maintainable ORM-based approach while keeping the existing PostgreSQL adapter intact.

Describe the solution you'd like
Add a new SequelizeDatabaseClient class that implements the existing DatabaseAdapter interface using Sequelize ORM. This would provide:

• Model-based database operations instead of raw SQL
• Built-in connection pooling and transaction management
• Better TypeScript integration through Sequelize models
• Easier testing through Sequelize's test helpers
• Optional alternative to the current PostgreSQL adapter

Describe alternatives you've considered

• TypeORM: Less robust PostgreSQL support
• Prisma: Requires additional build steps
• Knex.js: Only query builder without ORM features
• Keeping only raw SQL: Less maintainable long-term

Additional context
This would be an additive feature - the existing PostgreSQL adapter would remain untouched and developers could choose which implementation to use. The Sequelize client would follow the same interface and maintain compatibility with all current features including vector operations.

[github-actions]

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