exportPdf passed the raw map_blueprint_light setting value, which is a
root-relative /api path. Under /ops or /shopdb that resolves to the server
root and 404s, so the export died with "Failed to load blueprint image".
The on-screen map was unaffected because it goes through blueprintUrlFor,
which applies withBase - use that here too.
Same file, so this also carries the subtype auto-palette replacement that
goes with the marker-legibility change in the next commit.
d5635a4306