1.5.0 — Fixes: cron email attachment, settings errors display, shared validators

Fixed

• Cron email attachment: the monthly backup email now attaches the latest backup file. Previously WP-Cron's empty-string argument caused func_get_args() to be non-empty, so the email was sent with no attachment (includes/class-udc-email-sync.php).
• Settings errors display: the settings page now calls settings_errors(), so admins see the rejection messages produced by the sanitize callbacks (e.g. invalid Google Drive credentials or colors) instead of a silent failure (includes/class-udc-settings.php).

Refactored

• Deduplicated the date, datetime, time, and length validators into a new shared UDC_Validation class (includes/udc-validation.php), now used by both the shortcode submission handler and the backup restore path.

Housekeeping

• Version bumped to 1.5.0 (plugin header and UDC_DB_VERSION).