dc:subject is Adobe's "Keywords" panel, but PhotoPrism's Keywords,
Labels, and Subject fields serve distinct purposes. Route dc:subject to
the descriptive Details.Subject field only (matching the embedded/
ExifTool path, where data.Subject comes from the dc:subject-backed
Subject tag and data.Keywords from IPTC Keywords), never the Keywords
field. Multi-word entries keep their spaces; the value stays searchable
via IndexKeywords and still drives label matching.