sslip.io local wildcard install: instance editor fails (Invalid WebSocket frame: RSV1 must be clear)

### Current Behavior

When running self-hosted FlowFuse using the documented sslip.io wildcard domain option (no local DNS server), opening a hosted instance editor causes repeated websocket errors and the editor does not load/work correctly.

Ideally I need an answer within a week on this. This method is in our docs:
https://flowfuse.com/docs/install/dns-setup/#no-local-dns-server

### Expected Behavior

[warn] Communication channel error: RangeError: Invalid WebSocket frame: RSV1 must be clear
Editor fails to function correctly.

### Steps To Reproduce

1. Deploy FlowFuse via Docker Compose
2. Configure domain using 127.0.0.1.sslip.io (per docs “No local DNS server”)
3. Create/start a hosted instance
4. Open the instance editor

### Environment

- FlowFuse: v2.26.2
- Docker Desktop (macOS)
- sslip.io wildcard domain setup

### Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate