layouts: keep every content viewport's wires cached (#1769)

The resident wire sets were capped at 16 and cleared once more were
held. A layout with more content viewports than that (24 in the report)
cleared them all on each redraw and re-tessellated the model for every
viewport, so the layout stayed sluggish even when nothing changed. The
cap now covers the shown layout's viewports: idle redraws build no
wires, and a frame of that layout draws in ~14 ms instead of ~30 ms
plus ~100 ms of rebuilds.

The automation bridge gains a `layout_switch` action, as clicking a
layout tab does, which is how this was measured.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/control/actions.rs

@@ -1166,6 +1166,8 @@ impl OpenCADStudio {
         let name = string(req, "name")?;
         let msg = match name {
             "close_modal" => Message::CloseModal,
+            // Show a layout (or "Model"), as clicking its tab does.
+            "layout_switch" => Message::LayoutSwitch(string(req, "value")?.into()),
             // The "changed outside" modal's suggested actions (D6): reload
             // the disk copy, keep the in-memory one and overwrite, save as,
             // or dismiss. Native only — the web build has no such dialog.