Generate and host a production IIIF manifest for the Liber Usualis

Manuscript.manifest_url needs to point at a real, stably-hosted IIIF Presentation manifest (confirmed this is live-fetched server-side by ManifestProxyView on every request, not cached or validated ahead of time).

Locally, a manifest was hand-generated (one canvas per page, with real image dimensions) and served via nginx's own /local_manifests location as a stopgap, since the Liber Usualis has no manifest hosted externally. Production needs a proper, maintainable generation and hosting approach -- this probably shouldn't be a one-off hand-generated file long-term.

Start by reading ManifestProxyView and the current Manuscript.manifest_url handling, then inspect the nginx /local_manifests stopgap and the hand-generated manifest. The work is done when a maintainable production process generates and hosts a stable IIIF manifest for every Liber Usualis page, with real image dimensions, and manifest_url points to it.

Written by the indexing model from the issue text.