Update the editable per-design system-loss settings.

The request body is a flat map of loss name to percentage. Only the losses you supply are
updated; all others are left unchanged (partial update). Values are percentages between 0
and 100, accepted to one decimal place.

Updating system losses invalidates the design's performance simulation. This endpoint
does not re-run the simulation — run it separately to recompute production. Until then,
energy_production.up_to_date on the Design Summary will be
false.

Locks

Some losses cannot be edited and a request to change them is rejected with 422:

• Financing lock — when a financing product is selected for the design, that product
  dictates every loss. The whole update is rejected. This is reflected on read as
  editable: false / locked_by_financier: "<code>", with every field locked: true and
  disabled_reason: "financier".
• Shading-engine lock — when the shading engine is enabled, the shading loss is
  computed automatically and cannot be set manually. A request including shading is
  rejected, and on read that field is locked: true with
  disabled_reason: "shading_engine_enabled".

Mapping to loss_summary stages

Each editable setting affects exactly one loss_summary output stage on the Design Summary:

The remaining loss_summary stages are engine-computed and have no editable input.