feat(lib): add require_disk_space helper and enforce pre-flight disk checks

- add `require_disk_space` function to lib/common.sh with dedup logic for shared filesystems
- gate cloudpanel, coolify, pterodactyl installs behind a 2–3 GB disk check
- gate uptime-kuma, proxmox update, harden, update-server, and server-benchmark behind 300–1024 MB disk checks
- fail early with a clear error before apt installs or config writes can leave the system in a partial state

apps/uptime-kuma.sh

@@ -93,7 +93,9 @@ install_uptime_kuma() {
         echo -e "${YELLOW}Uptime Kuma is already installed!${NC}"
         return 0
     fi
-    
+
+    require_disk_space 1024 || return 1
+
     echo "[1/4] Installing dependencies..."
     install_dependencies
     echo ""