The foundation for the 'Scan Video Library' automation (the video twin of music's
Scan Library). PlexVideoSource.refresh_sections() triggers a Plex scan on the selected
movie/TV sections (section.update()); JellyfinVideoSource.refresh_sections() POSTs
/Items/{id}/Refresh per selected video view (the GET-only _make_request can't POST).
Module helper refresh_video_server_sections() gets the active source and refreshes —
scoped to the user's chosen video libraries (Settings), so it scans the CORRECT media,
not music. Video-only, additive; isolation guard + (my code) ruff clean.
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