V53 PERIMETER HALO SECONDARY DEFORMATION

What changed
- Replaced the v52 one-sided halo band with a perimeter halo around the whole continuous fault footprint.
- Secondary deformation now decays outward from the rounded rupture support boundary itself.
- The field is still biased to be stronger on the selected subsidence side, but no longer depends on a mostly parallel side band.
- This should reduce the remaining stripe-like look and feel closer to a manually brushed secondary deformation zone.

Why
- The previous version still looked like a ribbon because the dominant amplitude was tied mainly to the fault-normal direction.
- The target pattern is a softer cloud / halo around the main deformation band, with side preference but without a detached long stripe.

Operational notes
- Press G to regenerate the automatic secondary deformation field after editing the finite-fault model.
- If the preferred subsidence side is flipped, use D and regenerate again.

Implementation note
- This remains an empirical shape model, not a full elastic dislocation solution.
