fix(makefile): set help as default target instead of parameter error

- Add .DEFAULT_GOAL := help to make 'make' show help by default
- Previously 'make' without arguments showed parameter validation error
- Now provides better UX by showing comprehensive help output
- Preserves parameter validation for infrastructure commands that need them
- Fixes common user frustration when exploring available commands

Improves developer experience for Issue #28 staging deployment testing.

Author: josecelano

Makefile

@@ -9,18 +9,14 @@
 .PHONY: vm-ssh vm-console vm-gui-console vm-clean-ssh vm-prepare-ssh vm-status
 .PHONY: dev-setup dev-deploy dev-test dev-clean
 
-# Default variables
-VM_NAME ?= torrust-tracker-demo
-# Defaults for quick development workflows only
-DEV_ENVIRONMENT_TYPE ?= development
-DEV_ENVIRONMENT_FILE ?= development-libvirt
-DEV_PROVIDER ?= libvirt
-TERRAFORM_DIR = infrastructure/terraform
-INFRA_TESTS_DIR = infrastructure/tests
-TESTS_DIR = tests
-SCRIPTS_DIR = infrastructure/scripts
-
-# Parameter validation for infrastructure commands
+# Default environment variables
+ENVIRONMENT_TYPE ?= development
+ENVIRONMENT_FILE ?= development-libvirt
+
+# Default target - show help when no target specified
+.DEFAULT_GOAL := help
+
+# Parameter validation target
 check-infra-params:
 	@if [ -z "$(ENVIRONMENT_TYPE)" ]; then \
 		echo "❌ Error: ENVIRONMENT_TYPE not specified"; \