Web IDE WebSocket 404 errors due to CDN Origin not in allowed origins
### Summary
WebSocket connections in the Web IDE fail with 404 errors due to mismatched `Origin` headers from the Web IDE CDN (`*.cdn.web-ide.gitlab-static.net`).
This is related to the ActionCable allowed origins configuration introduced to fix websocket issues in Geo environments, see https://gitlab.com/gitlab-org/gitlab/-/issues/579074#note_2922948141
I am unsure if WebSockets are used in the Web IDE - if they are then we should address this.
### Steps to reproduce
1. Navigate to any project and open the Web IDE
2. Open browser Developer Tools and check the Network tab
3. Observe WebSocket connection attempts to `/-/cable`
### Example Project
This can be reproduced on any GitLab project when using the Web IDE.
### What is the current _bug_ behavior?
WebSocket connections from the Web IDE fail with 404 errors. The logs show:
```
{"backend_id":"rails","content_type":"text/plain; charset=utf-8","correlation_id":"01KBBXH5DM6ZTH553VDHC3BATN","duration_ms":26,"host":"unified.example.com","level":"info","method":"GET","msg":"access","proto":"HTTP/1.1","read_bytes":1340,"referrer":"","remote_addr":"x.x.x.x:0","remote_ip":"x.x.x.x","route":"^/-/cable\\z","route_id":"action_cable","status":404,"system":"http","time":"2025-12-01T02:58:06Z","ttfb_ms":26,"uri":"/-/cable","user_agent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/142.0.0.0 Safari/537.36","written_bytes":14}
```
Also see https://log.gprd.gitlab.net/app/r/s/sDdTA, although I cannot confirm if all of these requests are related to the Web IDE.
The Web IDE sends requests with an Origin header from `*.cdn.web-ide.gitlab-static.net`, which is not included in the ActionCable allowed origins configuration.
### What is the expected _correct_ behavior?
WebSocket connections from the Web IDE should succeed.
### Relevant logs and/or screenshots
{width=654 height=600}
Workhorse logs showing 404 responses for `/-/cable` requests from the Web IDE.
### Output of checks
This bug happens on GitLab.com and self-managed
### Possible fixes
The Web IDE uses a CDN with origins like `*.cdn.web-ide.gitlab-static.net`.
Do we need to allow this origin in [`config/initializers/action_cable.rb#L10`](https://gitlab.com/gitlab-org/gitlab/-/blob/fd7b63154a7160354f254d9939b73e02fdb3e559/config/initializers/action_cable.rb#L10)?
Related to #579074 and !212819.
issue