Add aftersales work order feature

- AftersalesOrder model with state machine (created/pending_confirmation/closed/rejected)
- Public scan-to-confirm flow with phone last-4 verification and rate limiting
- Technician role and middleware for ownership-scoped operations
- QR code generation pointing to /aftersales/{serialNumber}
- Admin overrides: reassign, force-close, delete

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

database/database.go

@@ -114,6 +114,7 @@ func AutoMigrate() {
 		&models.Company{},
 		&models.Serial{},
 		&models.EmployeeSerial{},
+		&models.AftersalesOrder{},
 	); err != nil {
 		logger.Fatal("数据库迁移失败", logger.Err(err))
 	}