Improved: CIDR Calculator (/tools/cidr-calculator.php) — added an "Export to .txt" button on the…

CIDR Calculator (/tools/cidr-calculator.php) — added an "Export to .txt" button on the results panel. Downloads a plain-text report of the calculated network, address details, range, dotted-binary representation, and quick reference. Filename pattern: cidr-<network>_<prefix>.txt. 100% client-side — nothing is sent to the server.