[Self-hosted] System DMs fail to send when instance DMs are disabled

Reproduction steps

Go to your instance's admin panel - Instance domain + /admin in the browser
Sign in with an account with admin access
In the sidebar, under Configuration, go to Instance Config - /admin/instance-config.
Under Community & policy and Direct messages, friends and personal notes, disable Direct messages.
May not be necessary but I restarted Fluxer to make sure it applied correctly after trying system DMs. - rexctl restart (I did stop start but restart would be quicker)
In the sidebar, under Content Tools, go to System DMs - /admin/system-dms.
To send a system DM, set Recipient user IDs to either * for every account or enter your account ID, found by clicking your account at the top of the page and then under User ID.
Enter anything in Content and press Queue send
You will see Failed to send system DM.

Expected behaviour

I know the bug title sounds stupid because duh DMs are disabled but hear me out. The System DMs page could be disabled while DMs are disabled on the instance or the Failed to send system DM error message could say that DMs are disabled on this instance. Maybe system DMs could still be allowed when DMs are disabled on the instance?

Actual behaviour

System DMs page enabled while DMs are disabled on the instance and confusing Failed to send system DM error message if the instance admin has forgotten that instance DMs are disabled.

Build information

$ rexctl version rexctl 2026.1026.152924 Fluxer 2026.1026.152924 Stable Web 2026.1026.150452, Linux (x64), Firefox 158.0, Locale en-GB

Platform

Self-hosting