Media audit: check that server supports range requests

Range requests are required for smooth media playback performance and scrubbing. Range requests are supported by default by most servers, but there may be misconfiguration (e.g. by a hosting service) that means they're turned off.

If a page has an audio or video element, check that range requests are supported by the server serving the media.

To test, make a head request for a media resource loaded by a media element on the page, then check that the response headers include `Accept-Ranges: bytes` (and not `Accept-Ranges: none`).

The issue identifies the desired audit behavior but names no file, test, or entry point. Locate the existing media-audit checks and their tests, then trace how media resources and HEAD response headers are handled. Done means audio and video resources are checked and the Accept-Ranges response is evaluated as described.

Written by the indexing model from the issue text.