feat: add data access layer (repositories)

- Add user repository with CRUD operations and authentication methods
- Add session repository for session management and validation
- Add API key repository for API key management
- Include proper error handling and database transaction support
- Implement search and filtering capabilities

repositories/user.go

@@ -0,0 +1,66 @@
+package repositories
+
+import (
+	"git.secnex.io/secnex/idp-api/models"
+	"gorm.io/gorm"
+)
+
+type UserRepository struct {
+	db *gorm.DB
+}
+
+func NewUserRepository(db *gorm.DB) *UserRepository {
+	return &UserRepository{db: db}
+}
+
+// GetAllUsers retrieves all users from the database
+func (r *UserRepository) GetAllUsers() ([]models.User, error) {
+	var users []models.User
+	err := r.db.Find(&users).Error
+	return users, err
+}
+
+// GetUserByID retrieves a user by ID
+func (r *UserRepository) GetUserByID(id string) (*models.User, error) {
+	var user models.User
+	err := r.db.First(&user, "id = ?", id).Error
+	if err != nil {
+		return nil, err
+	}
+	return &user, nil
+}
+
+// CreateUser creates a new user
+func (r *UserRepository) CreateUser(user *models.User) error {
+	return r.db.Create(user).Error
+}
+
+// UpdateUser updates an existing user
+func (r *UserRepository) UpdateUser(user *models.User) error {
+	return r.db.Save(user).Error
+}
+
+// DeleteUser deletes a user by ID
+func (r *UserRepository) DeleteUser(id string) error {
+	return r.db.Delete(&models.User{}, "id = ?", id).Error
+}
+
+// GetUserByEmail retrieves a user by email
+func (r *UserRepository) GetUserByEmail(email string) (*models.User, error) {
+	var user models.User
+	err := r.db.First(&user, "email = ?", email).Error
+	if err != nil {
+		return nil, err
+	}
+	return &user, nil
+}
+
+// GetUserByUsername retrieves a user by username
+func (r *UserRepository) GetUserByUsername(username string) (*models.User, error) {
+	var user models.User
+	err := r.db.First(&user, "username = ?", username).Error
+	if err != nil {
+		return nil, err
+	}
+	return &user, nil
+}