Backend Nest Config

Objective

Structure the shared NestJS backend layer, preferably under apps/backend/src/shared/, to centralize API error handling, JWT authentication, guards, decorators, and reusable types for controllers and protected endpoints.

This skill exists to remove repetition in controllers, avoid manual try/catch for domain errors, and create a secure, extensible foundation for authenticated routes while respecting the existing error hierarchy in packages/shared.

Mandatory readings

Before implementing, read the files listed in references/mandatory-readings.md.

This includes, at minimum: