Thanks for your posting! Great to hear that you enjoy the 5.2
Happy to add another vote to the attachment feature request for the API.
Regarding the attachments: it would be possible to access the attachments directly without going through TestRail and you would need to make the attachment directory publicly accessible via your web server configuration. We usually don't recommend this as TestRail's permissions wouldn't apply in this case but this would be an option. The attachments on disk have a different filename/URL when compared to accessing it through TestRail (attachments/view/###) though.
The better option and the one we would recommend though is giving your developers access to TestRail as well. In addition to having access to the screenshots, we found that this significantly improves the testing productivity of the entire team (as developers can give direct feedback in TestRail, set test statuses to Retest, see all test results, etc.).
I hope this helps!