Add initial backend implementation

- Go module with Gin, GORM, JWT, excelize dependencies
- Configuration loading from YAML with all settings
- GORM models for users, categories, components, configurations, alerts
- Repository layer for all entities
- Services: auth (JWT), pricing (median/average/weighted), components,
  quotes, configurations, export (CSV/XLSX), alerts
- Middleware: JWT auth, role-based access, CORS
- HTTP handlers for all API endpoints
- Main server with dependency injection and graceful shutdown

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/services/auth.go

@@ -0,0 +1,180 @@
+package services
+
+import (
+	"errors"
+	"time"
+
+	"github.com/golang-jwt/jwt/v5"
+	"github.com/mchus/quoteforge/internal/config"
+	"github.com/mchus/quoteforge/internal/models"
+	"github.com/mchus/quoteforge/internal/repository"
+	"golang.org/x/crypto/bcrypt"
+)
+
+var (
+	ErrInvalidCredentials = errors.New("invalid username or password")
+	ErrUserNotFound       = errors.New("user not found")
+	ErrUserInactive       = errors.New("user account is inactive")
+	ErrInvalidToken       = errors.New("invalid token")
+	ErrTokenExpired       = errors.New("token expired")
+)
+
+type AuthService struct {
+	userRepo *repository.UserRepository
+	config   config.AuthConfig
+}
+
+func NewAuthService(userRepo *repository.UserRepository, cfg config.AuthConfig) *AuthService {
+	return &AuthService{
+		userRepo: userRepo,
+		config:   cfg,
+	}
+}
+
+type TokenPair struct {
+	AccessToken  string `json:"access_token"`
+	RefreshToken string `json:"refresh_token"`
+	ExpiresAt    int64  `json:"expires_at"`
+}
+
+type Claims struct {
+	UserID   uint            `json:"user_id"`
+	Username string          `json:"username"`
+	Role     models.UserRole `json:"role"`
+	jwt.RegisteredClaims
+}
+
+func (s *AuthService) Login(username, password string) (*TokenPair, *models.User, error) {
+	user, err := s.userRepo.GetByUsername(username)
+	if err != nil {
+		return nil, nil, ErrInvalidCredentials
+	}
+
+	if !user.IsActive {
+		return nil, nil, ErrUserInactive
+	}
+
+	if err := bcrypt.CompareHashAndPassword([]byte(user.PasswordHash), []byte(password)); err != nil {
+		return nil, nil, ErrInvalidCredentials
+	}
+
+	tokens, err := s.generateTokenPair(user)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	return tokens, user, nil
+}
+
+func (s *AuthService) RefreshTokens(refreshToken string) (*TokenPair, error) {
+	claims, err := s.ValidateToken(refreshToken)
+	if err != nil {
+		return nil, err
+	}
+
+	user, err := s.userRepo.GetByID(claims.UserID)
+	if err != nil {
+		return nil, ErrUserNotFound
+	}
+
+	if !user.IsActive {
+		return nil, ErrUserInactive
+	}
+
+	return s.generateTokenPair(user)
+}
+
+func (s *AuthService) ValidateToken(tokenString string) (*Claims, error) {
+	token, err := jwt.ParseWithClaims(tokenString, &Claims{}, func(token *jwt.Token) (interface{}, error) {
+		return []byte(s.config.JWTSecret), nil
+	})
+
+	if err != nil {
+		if errors.Is(err, jwt.ErrTokenExpired) {
+			return nil, ErrTokenExpired
+		}
+		return nil, ErrInvalidToken
+	}
+
+	claims, ok := token.Claims.(*Claims)
+	if !ok || !token.Valid {
+		return nil, ErrInvalidToken
+	}
+
+	return claims, nil
+}
+
+func (s *AuthService) generateTokenPair(user *models.User) (*TokenPair, error) {
+	now := time.Now()
+	accessExpiry := now.Add(s.config.TokenExpiry)
+	refreshExpiry := now.Add(s.config.RefreshExpiry)
+
+	accessClaims := &Claims{
+		UserID:   user.ID,
+		Username: user.Username,
+		Role:     user.Role,
+		RegisteredClaims: jwt.RegisteredClaims{
+			ExpiresAt: jwt.NewNumericDate(accessExpiry),
+			IssuedAt:  jwt.NewNumericDate(now),
+			Subject:   user.Username,
+		},
+	}
+
+	accessToken := jwt.NewWithClaims(jwt.SigningMethodHS256, accessClaims)
+	accessTokenString, err := accessToken.SignedString([]byte(s.config.JWTSecret))
+	if err != nil {
+		return nil, err
+	}
+
+	refreshClaims := &Claims{
+		UserID:   user.ID,
+		Username: user.Username,
+		Role:     user.Role,
+		RegisteredClaims: jwt.RegisteredClaims{
+			ExpiresAt: jwt.NewNumericDate(refreshExpiry),
+			IssuedAt:  jwt.NewNumericDate(now),
+			Subject:   user.Username,
+		},
+	}
+
+	refreshToken := jwt.NewWithClaims(jwt.SigningMethodHS256, refreshClaims)
+	refreshTokenString, err := refreshToken.SignedString([]byte(s.config.JWTSecret))
+	if err != nil {
+		return nil, err
+	}
+
+	return &TokenPair{
+		AccessToken:  accessTokenString,
+		RefreshToken: refreshTokenString,
+		ExpiresAt:    accessExpiry.Unix(),
+	}, nil
+}
+
+func (s *AuthService) HashPassword(password string) (string, error) {
+	hash, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
+	if err != nil {
+		return "", err
+	}
+	return string(hash), nil
+}
+
+func (s *AuthService) CreateUser(username, email, password string, role models.UserRole) (*models.User, error) {
+	hash, err := s.HashPassword(password)
+	if err != nil {
+		return nil, err
+	}
+
+	user := &models.User{
+		Username:     username,
+		Email:        email,
+		PasswordHash: hash,
+		Role:         role,
+		IsActive:     true,
+	}
+
+	if err := s.userRepo.Create(user); err != nil {
+		return nil, err
+	}
+
+	return user, nil
+}