Refactor disk-usage logic into dedicated script

Move disk-usage functionality from Makefile to a dedicated shell script
for better maintainability and consistency with other scripts.

Changes:
- Create scripts/disk-usage.sh with all disk usage logic
- Simplify Makefile disk-usage target to call the script
- Add environment loading and color formatting to script
- Fix duplicate output by adding head -1 to grep chain

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Makefile

@@ -56,20 +56,7 @@ info: ## Affiche les informations sur le repository
 	@sudo bash -c 'set -a && source /etc/borgmatic/.env && set +a && borgmatic info'
 
 disk-usage: ## Affiche l'espace disque utilisé et libre sur le serveur de backup
-	@echo "$(BLUE)Espace disque sur le serveur de backup:$(NC)"
-	@echo ""
-	@echo "$(YELLOW)Espace utilisé par le repository Borg (toutes archives):$(NC)"
-	@sudo bash -c 'set -a && source /etc/borgmatic/.env && set +a && borgmatic info 2>/dev/null | grep "All archives" | grep GB'
-	@echo ""
-	@echo "$(YELLOW)Espace libre sur le serveur distant:$(NC)"
-	@sudo bash -c 'set -a && source /etc/borgmatic/.env && set +a && \
-		USER_HOST=$$(echo $$BORG_REPO | sed "s|ssh://||" | sed "s|:.*||") && \
-		PORT=$$(echo $$BORG_REPO | grep -o ":[0-9]*/" | sed "s|[:/]||g") && \
-		if [ -n "$$PORT" ]; then \
-			ssh -p $$PORT $$USER_HOST "df -h ~/ | tail -1"; \
-		else \
-			ssh $$USER_HOST "df -h ~/ | tail -1"; \
-		fi'
+	@sudo ./scripts/disk-usage.sh
 
 restore: ## Lance le script de restauration interactive
 	@echo "$(BLUE)Restauration interactive...$(NC)"