The elevated surface tokens (--bg-elevated / --surface-elevated) are
translucent, so sticky modal footers and table headers double-composited
over the modal surface and showed a visible lighter seam in light themes.
Add derived opaque tokens (--bg-elevated-solid / --surface-elevated-solid,
aliased as --lora-surface-solid) and use them for .modal-content, the
download/import modal sticky action footers, and the refresh result
table's sticky header, so the modal surface and its sticky layers always
share one opaque color across every theme and preset.