Add Nest-based user server with JWT authentication

[DmPrkp]

Summary

• add a dedicated NestJS user-server with Prisma, authentication modules, and validation
• define a Prisma user model, migrations, and seed script that provisions a default user with id 1
• expose sign-in and log-in endpoints that hash passwords and issue JWT access tokens, and wire the service into dev/prod docker compose

Testing

• not run (not requested)

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Codex Task