Implement Integration Tests for PostgreSQL Triggers

[Fatimasanusi]

Our database relies on PostgreSQL triggers to automatically update the updated_at timestamps and calculate moving averages. These need dedicated integration tests to ensure data integrity during schema migrations.

Acceptance Criteria:

• Create a Jest test suite that connects to an ephemeral PostgreSQL container.
• Write tests verifying that row modifications successfully fire the update_timestamp trigger.
• Write tests verifying the moving average calculation trigger behaves correctly on trade inserts.