test: setup integration test infrastructure and persistence typing

[heitorrsdev]

Description

This PR introduces the foundational integration testing infrastructure and strengthens the persistence layer with typed database access and structured PostgreSQL error mapping.

It establishes a deterministic PostgreSQL test environment, adds domain-level integration tests for reservations, and improves repository safety and ergonomics via Drizzle schema injection and centralized database error translation.

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What was done

• Added isolated PostgreSQL Docker environment for integration tests
• Implemented Jest bootstrap and deterministic test database lifecycle (reset/migrate/truncate)
• Integrated test workflows into Makefile and CI pipeline
• Added user and barber test factories for database seeding
• Injected Drizzle schemas into the database provider for full TypeScript typing
• Added PostgresErrorMapper to translate DB errors into domain errors
• Added findById method to Reservation repository
• Implemented integration tests for reservation invariants (persistence + conflict constraint)

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Why

• To enable real integration testing against PostgreSQL with deterministic state
• To ensure domain invariants (reservation conflicts) are enforced at the database layer
• To improve repository DX and type safety with Drizzle schema injection
• To centralize database error translation and keep repositories clean
• To enforce automated test execution in CI and local workflows

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Notes

• This PR focuses on infrastructure and the first integration test suite, not full domain test coverage
• Concurrency tests for reservation conflicts will be added in a follow-up PR
• testing.md documentation will be introduced separately to keep this PR focused