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/update-server.sh

@@ -62,6 +62,8 @@ if ! command -v apt-get >/dev/null 2>&1; then
     exit 1
 fi
 
+require_disk_space 1024 || exit 1
+
 UPGRADE_CMD="upgrade"
 UPGRADE_LABEL="Upgrade installed packages"
 if [ $DO_FULL_UPGRADE -eq 1 ]; then