Reorganized repository into backend and frontend directories

backend/internal/model/user.go

@@ -0,0 +1,12 @@
+package model
+
+import (
+	"gorm.io/gorm"
+)
+
+// User represents a registered user in the system.
+type User struct {
+	gorm.Model
+	Username string `gorm:"uniqueIndex;not null"`
+	Password string `gorm:"not null"` // Hashed password
+}