fix: correct domain configuration in environment defaults

**Domain Configuration Fixes:**
- staging.defaults: DOMAIN_NAME 'tracker.torrust-demo.dev' → 'torrust-demo.dev'
- production.defaults: DOMAIN_NAME 'tracker.torrust-demo.com' → 'torrust-demo.com'

**System Behavior:**
- Current implementation automatically adds 'tracker.' and 'grafana.' subdomains
- DOMAIN_NAME should contain only the base domain (e.g., torrust-demo.dev)
- Services become: tracker.torrust-demo.dev, grafana.torrust-demo.dev

**Documentation Updates:**
- Add comprehensive domain configuration behavior section
- Document current subdomain auto-prefix behavior
- Note future improvement to allow full domain specification
- Fix examples in staging/production environment sections

**Environment Regeneration:**
- Regenerated staging-hetzner.env with correct domain
- Regenerated production-hetzner.env with correct domain

This fixes the core domain configuration issue discovered during staging setup.

Author: josecelano

docs/guides/deployment-guide.md

@@ -805,6 +805,32 @@ echo "Updated $SUBDOMAIN.$DOMAIN A record to $NEW_IP"
 
 ## 🚀 Part 4: Environment Configuration
 
+### Domain Configuration Behavior
+
+**Important**: The current system automatically adds subdomain prefixes to the main domain
+configured in `DOMAIN_NAME`.
+
+#### Current Behavior
+
+When you configure:
+
+```bash
+DOMAIN_NAME=torrust-demo.dev
+```
+
+The system automatically creates:
+
+- **Tracker service**: `tracker.torrust-demo.dev`
+- **Grafana service**: `grafana.torrust-demo.dev`
+
+#### Required Domain Configuration
+
+- **Staging**: `DOMAIN_NAME=torrust-demo.dev`
+- **Production**: `DOMAIN_NAME=torrust-demo.com`
+
+> **Note**: Future improvements will allow declaring full domain names for each service
+> independently, but this is the current implementation that must be followed.
+
 ### Development Environment Configuration
 
 #### Local Environment Variables
@@ -939,7 +965,7 @@ VM_LOCATION=nbg1  # Nuremberg
 VM_IMAGE=ubuntu-24.04
 
 # === DOMAIN CONFIGURATION ===
-DOMAIN_NAME=tracker.torrust-demo.dev
+DOMAIN_NAME=torrust-demo.dev
 GRAFANA_DOMAIN=grafana.torrust-demo.dev
 
 # === SSL CONFIGURATION ===
@@ -986,7 +1012,7 @@ VM_LOCATION=nbg1  # Nuremberg
 VM_IMAGE=ubuntu-24.04
 
 # === DOMAIN CONFIGURATION ===
-DOMAIN_NAME=tracker.torrust-demo.com
+DOMAIN_NAME=torrust-demo.com
 GRAFANA_DOMAIN=grafana.torrust-demo.com
 
 # === SSL CONFIGURATION ===

infrastructure/config/templates/environments/production.defaults

@@ -13,10 +13,10 @@ MYSQL_PASSWORD="REPLACE_WITH_SECURE_PASSWORD"
 TRACKER_TOKEN_DESCRIPTION=" (Used for administrative API access)"
 TRACKER_ADMIN_TOKEN="REPLACE_WITH_SECURE_ADMIN_TOKEN"
 GF_SECURITY_ADMIN_PASSWORD="REPLACE_WITH_SECURE_GRAFANA_PASSWORD"
-DOMAIN_NAME_DESCRIPTION=" (required for production)"
-DOMAIN_NAME="REPLACE_WITH_YOUR_DOMAIN"
-CERTBOT_EMAIL_DESCRIPTION="Let's Encrypt certificate registration (required for production)"
-CERTBOT_EMAIL="REPLACE_WITH_YOUR_EMAIL"
+DOMAIN_NAME_DESCRIPTION=" (production domain)"
+DOMAIN_NAME="torrust-demo.com"
+CERTBOT_EMAIL_DESCRIPTION="Let's Encrypt certificate registration (production domain)"
+CERTBOT_EMAIL="admin@torrust-demo.com"
 ENABLE_SSL_DESCRIPTION=" (true for production, false for testing)"
 ENABLE_SSL="true"
 BACKUP_DESCRIPTION=" (true/false)"

infrastructure/config/templates/environments/staging.defaults

@@ -0,0 +1,36 @@
+# Staging Environment Default Values  
+# These values are used to generate staging.env template from the base template
+# Contains placeholder values that must be replaced with secure secrets
+
+ENVIRONMENT_DESCRIPTION="Staging Environment Configuration Template"
+ENVIRONMENT_INSTRUCTIONS="Copy this file to staging.env and replace placeholder values with secure secrets"
+ENVIRONMENT="staging"
+
+# === VM CONFIGURATION ===
+VM_NAME="torrust-tracker-staging"
+VM_MEMORY="4096"
+VM_VCPUS="4"
+VM_DISK_SIZE="30"
+PERSISTENT_DATA_SIZE="30"
+SSH_PUBLIC_KEY=""  # Leave empty - auto-detected during deployment
+USE_MINIMAL_CONFIG="false"
+
+TEMPLATE_PROCESSING_VARS=""
+SECRETS_DESCRIPTION="
+# IMPORTANT: Replace ALL placeholder values with actual secure secrets before deployment!"
+MYSQL_ROOT_PASSWORD="REPLACE_WITH_SECURE_ROOT_PASSWORD"
+MYSQL_PASSWORD="REPLACE_WITH_SECURE_PASSWORD"
+TRACKER_TOKEN_DESCRIPTION=" (Used for administrative API access)"
+TRACKER_ADMIN_TOKEN="REPLACE_WITH_SECURE_ADMIN_TOKEN"
+GF_SECURITY_ADMIN_PASSWORD="REPLACE_WITH_SECURE_GRAFANA_PASSWORD"
+DOMAIN_NAME_DESCRIPTION=" (staging domain for testing)"
+DOMAIN_NAME="torrust-demo.dev"
+CERTBOT_EMAIL_DESCRIPTION="Let's Encrypt certificate registration (staging domain)"
+CERTBOT_EMAIL="admin@torrust-demo.dev"
+ENABLE_SSL_DESCRIPTION=" (true for testing SSL automation)"
+ENABLE_SSL="true"
+BACKUP_DESCRIPTION=" (enabled with shorter retention for staging)"
+ENABLE_DB_BACKUPS="true"
+BACKUP_RETENTION_DAYS="3"
+USER_ID_DESCRIPTION=" (match host user)"
+USER_ID="1000"