selfhosted buzz relay, mobile paring is not working

**Describe the bug**
i setup via railway a whole buzz relay instance (with the one click solution you offering), when i try to connect my phone through the mobile qr code functionality within the already connected desktop client i just get a error message:
"WebSocket connection failed: HTTP error: 404 Not Found"

**Steps to reproduce**
1. Go to 'Settings Area' of your selfhosted community via desktop client
2. Click on 'mobile'
3. click on 'Start paring'
4. you directly see the error message

**Expected behavior**
that i can connect my phone easily with the qr code functionality through my selfhosted instance

**Version and platform**
Find your version at the bottom of the Settings sidebar. Write "unknown" if you can't determine it.
- Buzz version: docker pull ghcr.io/block/buzz:sha256423deb60f696e57184bda45e3f136f07d3d181006de820d881c2c20a30d58892
- OS: desktop client = mac, mobile = ios

**Logs / additional context**
unfortunately no error log in the railway instance

Start from Settings > mobile > Start pairing in the desktop client and reproduce the WebSocket 404 against the Railway self-hosted deployment. Trace the pairing request between the desktop client, relay, and iOS client; done means the QR flow connects the phone without the 404 error.

Written by the indexing model from the issue text.