Add user schema and CRUD package

[ThorbjoernTasche]

Summary

• add the @beyond/user workspace package with a PostgreSQL users schema
• add CRUD operations for create, lookup, list, update, and delete
• return public user records only; password hashes are never selected or returned
• add Drizzle migration 0000_create-users.sql with unique username and email constraints
• update workspace and Drizzle configuration to use the shared package

Why

This introduces a reusable data model for users while keeping domain persistence code outside the API application. The password field is explicitly documented as a one-way hash supplied by the caller.

Validation

• bun install --frozen-lockfile
• bun run test — 6 passing tests across the gateway and user package
• bun run typecheck
• docker compose config --quiet
• bun run db:generate
• bun run db:migrate against ephemeral PostgreSQL
• live CRUD verification: create, find, update, list, and delete, with no password field in returned records