feat: add data models and API structures

- Add User model with authentication fields and validation
- Add Session model for managing user sessions
- Add API response structures for consistent API responses
- Include GORM tags for database mapping and validation

models/user.go

@@ -0,0 +1,36 @@
+package models
+
+import (
+	"time"
+
+	"github.com/google/uuid"
+	"gorm.io/gorm"
+)
+
+type User struct {
+	ID         uuid.UUID      `json:"id" gorm:"primaryKey;type:uuid;default:gen_random_uuid()"`
+	FirstName  string         `json:"first_name" gorm:"not null"`
+	LastName   string         `json:"last_name" gorm:"not null"`
+	Username   string         `json:"username" gorm:"not null;unique"`
+	Password   string         `json:"password" gorm:"not null"`
+	Email      string         `json:"email" gorm:"not null;unique"`
+	Enabled    bool           `json:"enabled" gorm:"not null;default:true"`
+	Verified   bool           `json:"verified" gorm:"not null;default:false"` // TODO: remove this field
+	SuperAdmin bool           `json:"super_admin" gorm:"not null;default:false"`
+	CreatedAt  time.Time      `json:"created_at" gorm:"not null;default:now()"`
+	UpdatedAt  time.Time      `json:"updated_at" gorm:"not null;default:now()"`
+	DeletedAt  gorm.DeletedAt `json:"deleted_at" gorm:"index;default:null"`
+
+	// Relationships
+	ApiKeys  []ApiKey  `json:"api_keys" gorm:"foreignKey:user_id;references:id"`
+	Sessions []Session `json:"sessions" gorm:"foreignKey:user_id;references:id"`
+}
+
+func (u *User) TableName() string {
+	return "users"
+}
+
+func (u *User) BeforeCreate(tx *gorm.DB) (err error) {
+	u.ID = uuid.New()
+	return
+}