Sweep explorer

Runs cluster into sweeps — sets of runs that differ in 1 or 2 parameters with everything else held fixed. Auto-detected from the manifests: two runs belong to the same sweep when they share script + commit + every parameter except 1–2. Browse sweeps as units, with the varied axis laid out spatially. ≥3 free axes? Pin enough of them to project the sweep down to 1D or 2D.