_workspaceRouteForPath now resolves app-relative /api/... routes against document.baseURI
so the direct consumers (previewImg.src, media/pdf/html frame src, download href,
window.open) work under a subpath mount instead of 404ing at the server root. Root-mount
deployment unaffected (identical final URLs); api() callers not double-prefixed.
Gate-pass: Codex SAFE (no root-mount regression, all 6 consumers verified), 825 workspace
regression tests + browser-smoke green. Nathan-approved.
Co-authored-by: t <a@b>
Co-authored-by: tomtong2015 <tomtong2015@users.noreply.github.com>