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

tools/server-benchmark.sh

@@ -38,7 +38,9 @@ install_dependencies() {
     if ! command -v sysbench &> /dev/null; then
         echo -e "${YELLOW}[!] sysbench not found, installing...${NC}"
         echo ""
-        
+
+        require_disk_space 300 || return 1
+
         if command -v apt-get &> /dev/null; then
             run_spinner "Updating package list..." "apt-get update -qq"
             run_spinner "Installing sysbench..." "DEBIAN_FRONTEND=noninteractive apt-get install -y -qq sysbench"