Implements Task 5. Disables telnet/ftp/www/www-ssl/api/api-ssl (winbox kept
for recovery), sets DNS + NTP client, ensures SSH on the configured port.
Verified run-twice idempotent (changed=0) against crs310-maker on the bench.
Also sets ansible_user=sjat in host_vars for day-2 key auth.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>