Create a Go User Authentication Service

Problem/Feature Description

A SaaS company needs a user authentication microservice in Go. The service handles user registration, login (returning JWT tokens), and profile retrieval. It stores user data in a database and hashes passwords with bcrypt. The JWT signing key and database credentials must come from environment configuration.

The team wants clean architecture so different developers can work on handlers, business logic, and database code independently.

Output Specification

Produce a complete project structure with:

• go.mod with proper module path
• cmd/auth/main.go -- entry point that creates database connection, wires repository -> service -> handler, and starts HTTP server with graceful shutdown
• internal/config/config.go -- Config with PORT, DATABASE_URL, JWT_SECRET, JWT_EXPIRY_HOURS, LOG_LEVEL from environment
• internal/domain/models.go -- User (ID, Email, HashedPassword, Name, CreatedAt, UpdatedAt), RegisterRequest, LoginRequest, LoginResponse (with Token field), UserResponse (without password)
• internal/domain/errors.go -- AppError, NotFoundError, ValidationError, UnauthorizedError, ConflictError (duplicate email)
• internal/handler/ -- Handler struct, route registration, endpoints: POST /register, POST /login, GET /me (protected), writeJSON/writeError helpers, auth middleware that validates JWT
• internal/service/auth.go -- AuthService with Register (hash password, check duplicate), Login (verify password, generate JWT), GetUser; defines UserRepository interface
• internal/repository/users.go -- UserRepo implementing UserRepository with SQL queries
• Makefile with build, run, test, lint, tidy targets
• .gitignore for Go
• Test file internal/service/auth_test.go with table-driven tests for registration validation (empty email, duplicate email) and login (wrong password, success)