image rendering does not work

### What happened? Just upgraded grafana to 12.3.1 and found, that image export is not working at all: When clicking on the panel's `Export | Export as image | Generate image` I get immediately the error message: `Failed to generate image NetworkError when attempting to fetch resource.` ### What did you expect to happen? I should see least a request logged by the `./grafana-image-renderer server` running on the same server. ### Did this work before? Wasn't available before. ### How do we reproduce it? 1. Export 2. Export as image 3. Generate image ### Is the bug inside a dashboard panel? I guess it might be caused by inappropriate routing. E.g. in the "Firefox Developer GUI | Network" I see failed GET and OPTION requests like `http://localhost:3000/grafana/render/d/...` but the URL aka `Origin` used to access grafana is: `http://localhost:9147/grafana/d/...`. So my guess is, that the app uses either wrong hardcoded URLs, or does not use just URL pathes, but calculates by its own URLs in a buggy way by using wrong CGI/server params instead off `HTTP_HOST` for it. ### Environment (with versions)? Grafana: 12.3.1 OS: Ubuntu 24.04 Browser: Firefox 145.0.2 (64-bit) ### Grafana platform? A package manager (APT, YUM, BREW, etc.) ### Datasource(s)? _No response_