#8852: fix(matrix): Await mxcToHttp to properly detect authenticated media endpoint

## Problem The Matrix SDK's `getMediaEndpointPrefix()` method is async, but `mxcToHttp()` wasn't being awaited, causing it to return a Promise instead of the actual URL string. This resulted in improper media endpoint detection and download failures. ## Solution Add `await` to the `mxcToHttp()` call to properly detect the authenticated media endpoint: ```typescript const url = await params.client.mxcToHttp(params.mxcUrl); ``` ## Impact - Fixes media downloads on homeservers using MSC3916 authenticated media - Ensures proper endpoint selection (_matrix/media vs _matrix/client/v1/media) - No breaking changes for non-authenticated homeservers ## Related - MSC3916: Authenticated media - Part of Matrix media download improvements <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR updates Matrix media downloading to `await` the Matrix SDK’s async `mxcToHttp()` helper when determining the media endpoint prefix, preventing a Promise from being treated as a URL string. The change is localized to the Matrix media monitor code (`extensions/matrix/src/matrix/monitor/media.ts`) and aligns endpoint detection with MSC3916 authenticated media behavior while keeping download logic (via `downloadContent`) unchanged. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk. - The change is a single, correct await added to match an async API contract; it fixes a concrete runtime bug (Promise used where string expected) without altering downstream download/decrypt behavior. - No files require special attention <!-- greptile_other_comments_section --> <!-- /greptile_comment -->