Populate the assets/harnesses/ slots that the previous commit carved out.
Every row on the Alternative Agents scatter now renders as a composite
marker: the model provider logo on top and the harness logo on the bottom.

One small adjustment applied in-place to the four source SVGs: the
width/height attributes that hard-coded the rendered size to 1em were
stripped. Plotly's layout-image renderer doesn't establish a font-size
context, so 1em collapses to zero and the artwork renders as a speck in
the corner of the marker box. Removing those two attributes lets Plotly
size each SVG through its existing viewBox and the scatter's configured
sizex/sizey instead. No artwork was modified.

Smoke test: Alternative Agents view (7 rows) now produces 14 scatter
markers, every point is a full composite pair.