feat: RRBEC Local Server - Go backend with Django sync

- Implement local-first architecture with SQLite
- Add bidirectional sync with Django via ChangeLog
- JWT authentication with auto-refresh token
- REST API for products, orders, commands, payments
- Stock management with automatic deduction

rrbec_server/internal/models/models.go

@@ -0,0 +1,177 @@
+package models
+
+import (
+	"strconv"
+	"time"
+
+	"github.com/google/uuid"
+	"gorm.io/gorm"
+)
+
+// Custom type to handle Price as string or float from JSON
+type Price float64
+
+func (p *Price) UnmarshalJSON(data []byte) error {
+	if len(data) == 0 {
+		return nil
+	}
+	s := string(data)
+	// Remove quotes if it's a string
+	if s[0] == '"' {
+		s = s[1 : len(s)-1]
+	}
+	f, err := strconv.ParseFloat(s, 64)
+	if err != nil {
+		return err
+	}
+	*p = Price(f)
+	return nil
+}
+
+// Base model with UUID and sync fields
+type Base struct {
+	ID           uint      `gorm:"primaryKey" json:"id"`
+	UUID         string    `gorm:"uniqueIndex" json:"uuid"`
+	Sincronizado bool      `gorm:"default:false" json:"sincronizado"`
+	CreatedAt    time.Time `json:"created_at"`
+	UpdatedAt    time.Time `json:"updated_at"`
+}
+
+func (b *Base) BeforeCreate(tx *gorm.DB) (err error) {
+	if b.UUID == "" {
+		b.UUID = uuid.New().String()
+	}
+	return
+}
+
+type Mesa struct {
+	Base
+	Name     string `json:"name"`
+	Location string `json:"location"`
+	Active   bool   `gorm:"default:false" json:"active"`
+}
+
+type Client struct {
+	Base
+	Name      string    `json:"name"`
+	Debt      Price     `gorm:"default:0" json:"debt"`
+	CreatedAt time.Time `json:"created_at"`
+	Active    bool      `gorm:"default:true" json:"active"`
+	Contact   string    `json:"contact"`
+}
+
+type Category struct {
+	Base
+	Name   string `json:"name"`
+	Active bool   `gorm:"default:true" json:"active"`
+}
+
+type Product struct {
+	Base
+	Name          string  `json:"name"`
+	Description   string  `json:"description"`
+	Image         string  `json:"image"` // URL or Path
+	Price         Price   `json:"price"`
+	Quantity      int     `gorm:"default:0" json:"quantity"`
+	CategoryID    uint    `gorm:"column:category" json:"category"`
+	Cuisine       bool    `gorm:"default:false" json:"cuisine"`
+	Active        bool    `gorm:"default:true" json:"active"`
+	UnitOfMeasure *uint   `gorm:"column:unit_of_measure" json:"unit_of_measure"`
+}
+
+type ProductComponent struct {
+	Base
+	CompositeProductID uint    `json:"composite_product"`
+	ComponentProductID uint    `json:"component_product"`
+	QuantityRequired   float64 `json:"quantity_required"`
+}
+
+type Comanda struct {
+	Base
+	MesaID    uint       `json:"mesa"`
+	UserID    uint       `json:"user"`
+	TypePayID *uint      `json:"type_pay"`
+	ClientID  *uint      `json:"client"`
+	Name      string     `json:"name"`
+	Status    string     `json:"status"` // OPEN, CLOSED, FIADO
+	DtOpen    time.Time  `json:"dt_open"`
+	DtClose   *time.Time `json:"dt_close"`
+
+	// Nested items from Django (not stored in coma nda table)
+	Items []ProductComanda `gorm:"-" json:"items"`
+}
+
+type ProductComanda struct {
+	Base
+	ComandaID    uint      `json:"comanda"`
+	ProductID    uint      `json:"product"`
+	ProductName  string    `gorm:"-" json:"product_name"`  // Read-only
+	ProductPrice Price     `gorm:"-" json:"product_price"` // Read-only
+	DateTime     time.Time `json:"data_time"`
+	Applicant    string    `json:"applicant"`
+	Obs          string    `gorm:"-" json:"obs"` // From Order
+}
+
+type Order struct {
+	Base
+	ProductComandaID *uint      `json:"productComanda"`
+	ProductID        uint       `json:"id_product"`
+	ComandaID        uint       `json:"id_comanda"`
+	Obs              string     `json:"obs"`
+	Queue            time.Time  `json:"queue"`
+	Preparing        *time.Time `json:"preparing"`
+	Finished         *time.Time `json:"finished"`
+	Delivered        *time.Time `json:"delivered"`
+	Canceled         *time.Time `json:"canceled"`
+}
+
+func (o *Order) BeforeCreate(tx *gorm.DB) (err error) {
+	// Call Base.BeforeCreate to generate UUID
+	if err := o.Base.BeforeCreate(tx); err != nil {
+		return err
+	}
+	if o.Queue.IsZero() {
+		o.Queue = time.Now()
+	}
+	return
+}
+
+type TypePay struct {
+	Base
+	Name   string `json:"name"`
+	Active bool   `gorm:"default:true" json:"active"`
+}
+
+type Payment struct {
+	Base
+	Value       Price     `json:"value"`
+	TypePayID   uint      `json:"type_pay"`
+	ComandaID   uint      `json:"comanda"`
+	ClientID    *uint     `json:"client"`
+	Description string    `json:"description"`
+	DateTime    time.Time `json:"datetime"`
+}
+
+type User struct {
+	Base
+	Username  string `gorm:"uniqueIndex" json:"username"`
+	Password  string `json:"password"`
+	Email     string `json:"email"`
+	FirstName string `json:"first_name"`
+	LastName  string `json:"last_name"`
+	IsStaff   bool   `json:"is_staff"`
+	IsActive  bool   `json:"is_active"`
+}
+
+type SyncState struct {
+	ID         uint `gorm:"primaryKey"`
+	LastSyncID int  `gorm:"default:0"`
+}
+
+type ChangeLog struct {
+	ID        int       `json:"id"`
+	ModelName string    `json:"model_name"`
+	ObjectID  uint      `json:"object_id"`
+	Action    string    `json:"action"` // SAVE or DELETE
+	Timestamp time.Time `json:"timestamp"`
+}