The file viewer converts word-processor documents to PDF server-side via
LibreOffice (skald_core::docx::DocxConverter), mirroring the LaTeX pipeline
but content-hash cached: the format is self-contained, so there is no
dependency graph and the file watcher needs no expansion. Container-only
documents are shuttled out and converted on the host. With no LibreOffice
installed the viewer says so and falls back to download-only. Downloads
still save the original document, not the preview PDF.
