fix: disable default rspamd clamav integration when SKIP_CLAMD=y

[kvdb]

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Short Description

Disable the default Rspamd ClamAV integration when SKIP_CLAMD=y, so Rspamd stops trying to scan via clamd:3310 and no longer logs ClamAV timeout warnings.

Affected Containers

• rspamd-mailcow

Did you run tests?

What did you tested?

• Verified rspamd-mailcow receives SKIP_CLAMD
• Verified the hook creates /etc/rspamd/override.d/antivirus.conf
• Verified rspamadm configdump antivirus shows clamav { enabled = false; }
• Sent a test mail through SMTP on a live Mailcow setup
• Checked rspamd-mailcow logs before and after the change

What were the final results? (Awaited, got)

• Awaited: with SKIP_CLAMD=y, Rspamd should stop using the default ClamAV scanner and stop logging CLAM_VIRUS_FAIL / maximum retransmits exceed
• Got: the clamav module was disabled in effective config, and the test mail was processed without ClamAV timeout warnings or CLAM_VIRUS_FAIL

[milkmaker]

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