feat(layers): search boxes in the layer dropdown and Layer Manager (#343)

The ribbon layer dropdown gets a live search field above the list
(cleared when the dropdown closes, panel height tracks the filtered
count), and the Layer Manager toolbar gets one too. Both filter by
case-insensitive substring while toggle/rename messages keep the
original row indices, so acting on a filtered row hits the right layer.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/app/command_driver.rs

@@ -1578,7 +1578,7 @@ impl OpenCADStudio {
                             // window — the same points the grips expose — then
                             // refresh the stored measurement so the value tracks
                             // the stretched geometry.
-                            let mut mv = |p: &mut acadrust::types::Vector3| {
+                            let mv = |p: &mut acadrust::types::Vector3| {
                                 if in_win(p.x, p.y) {
                                     p.x += dx;
                                     p.y += dy;