chore: add make test, test-backend, test-frontend targets

- make test runs both backend and frontend tests
- make test-backend runs 'go test ./...'
- make test-frontend runs 'npm test'

Makefile

@@ -1,4 +1,4 @@
-.PHONY: backend frontend build run clean dev
+.PHONY: backend frontend build run clean dev test test-backend test-frontend
 
 # Default paths for dev — override via env
 SERVERFILE_DIR ?= ../dev-deploy/serverfiles
@@ -33,3 +33,11 @@ dev:
 clean:
 	rm -f backend/arma3-web-server
 	rm -rf frontend/dist backend/embed/dist
+
+test-backend:
+	cd backend && go test ./...
+
+test-frontend:
+	cd frontend && npm test
+
+test: test-backend test-frontend