Refactor customer domain structure and implement core entities, services, and handlers

- Introduced a flat structure for the customer domain, consolidating entities, aggregates, repositories, services, forms, and handlers into a single package.
- Added core entities: Customer and CustomerAggregate.
- Implemented request/response forms for customer authentication (Register, Login, Refresh Token, Change Password).
- Created CustomerService to handle business logic and data access through the Repository interface.
- Established CustomerHandler for HTTP request handling related to customer authentication.
- Removed previous domain structure artifacts to streamline the codebase.

internal/customer/entity.go

@@ -0,0 +1,22 @@
+package customer
+
+import (
+	"github.com/google/uuid"
+)
+
+// Customer represents a mobile app user (customer)
+type Customer struct {
+	ID           uuid.UUID `bson:"_id"`
+	Email        string    `bson:"email"`
+	Password     string    `bson:"password"` // Never serialize password
+	FirstName    string    `bson:"first_name"`
+	LastName     string    `bson:"last_name"`
+	Mobile       string    `bson:"mobile"`
+	CompanyID    uuid.UUID `bson:"company_id"`
+	IsActive     bool      `bson:"is_active"`
+	IsVerified   bool      `bson:"is_verified"`
+	DeviceTokens []string  `bson:"device_tokens"`           // For push notifications
+	LastLoginAt  *int64    `bson:"last_login_at,omitempty"` // Unix timestamp
+	CreatedAt    int64     `bson:"created_at"`              // Unix timestamp
+	UpdatedAt    int64     `bson:"updated_at"`              // Unix timestamp
+}