[M1] Add OpenAPI documentation for the V2 API

[rodrigolinhas]

Goal

Establish API documentation conventions early for the NestJS V2 backend.

Expected Scope

• Swagger/OpenAPI setup (@nestjs/swagger).
• API title, description, and version metadata.
• V2 endpoint discovery.
• Health/readiness documentation.
• First real migrated capability (Quotes) documented later in M1.

Acceptance Criteria

• OpenAPI document is generated from the NestJS application.
• API documentation can be accessed in development (e.g. /api/docs).
• M1 endpoints appear correctly.
• Request/response schemas are represented where applicable.
• Swagger setup does not expose secrets/configuration.

Dependencies

• Issue A ([M1] Bootstrap NestJS V2 backend #6): [M1] Bootstrap NestJS V2 backend.

Suggested PR

PR 3 — Health/readiness + OpenAPI + testing foundation (with Issues E and G)