fixed gorm shema for correct deletion and many2many relation beetween users and devices

server/internal/models/user_device.go

@@ -0,0 +1,13 @@
+package models
+
+import "time"
+
+type UserDevice struct {
+	UserID     uint   `gorm:"primaryKey;index;not null"`
+	DeviceGUID string `gorm:"primaryKey;size:64;index;not null"`
+	CreatedAt  time.Time
+
+	// Optional FKs with cascade (you already have cascade constraints on both sides)
+	User   User   `gorm:"constraint:OnDelete:CASCADE;"`
+	Device Device `gorm:"constraint:OnDelete:CASCADE;foreignKey:DeviceGUID;references:GUID"`
+}