Schema and Relations Consistency Improvements

The data model has been updated to improve relational consistency and alignment across services.

Changes include:

• Introduction of explicit junction tables for many-to-many relationships
• Standardization of relation naming across models and seeders

This reduces ambiguity in data access patterns and improves maintainability of both application logic and data pipelines.

The update also prepares the system for more complex relational queries required in traceability and audit scenarios.