新增设备别名管理功能，支持设备别名的保存与解绑

prisma/migrations/20260417070000_add_device_binding_alias/migration.sql

@@ -0,0 +1,2 @@
+ALTER TABLE "DeviceBinding"
+ADD COLUMN IF NOT EXISTS "alias" TEXT;

prisma/schema.prisma

@@ -90,6 +90,7 @@ model DeviceBinding {
   id            String           @id @default(cuid())
   caregiverId   String
   elderDeviceId String
+  alias         String?
   createdAt     DateTime         @default(now())
   caregiver     CaregiverAccount @relation(fields: [caregiverId], references: [id], onDelete: Cascade)
   elderDevice   ElderDevice      @relation(fields: [elderDeviceId], references: [id], onDelete: Cascade)