Add the Supplier entity to the schema

Problem Description

An online shop's NestJS + Drizzle project has two tables, category and product, created by the single migration apps/api/drizzle/migrations/0000_initial.sql. That migration has already been applied to the development, staging, and production databases, and its entry is recorded in apps/api/drizzle/migrations/meta/_journal.json.

The entity model at docs/entity_model.md has since been updated. It now contains a SUPPLIER entity and an optional relationship from PRODUCT to SUPPLIER, neither of which exists in the schema yet.

The database is shared with the rest of the team, so the migration history has to stay intact and replayable from scratch.

Output Specification

Bring the database schema in line with the updated entity model:

1. Add the SUPPLIER entity, with the attributes, defaults, and validation rules the entity model states.
2. Add the optional PRODUCT → SUPPLIER relationship described in the entity model.
3. Produce the migration that applies these changes to a database that already has 0000_initial.sql applied.