feat(editor): highlight edges and show preview import loader

- Highlight all edges connected to selected scene

- Show overlay spinner while uploading/optimizing preview image

- macOS: keep control window independent from presentation

Made-with: Cursor

app/renderer/editor/EditorApp.module.css

@@ -462,6 +462,46 @@
   display: flex;
   align-items: center;
   justify-content: center;
+  position: relative;
+}
+
+.previewBusyOverlay {
+  position: absolute;
+  inset: 0;
+  background: rgba(0, 0, 0, 0.55);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 12px;
+}
+
+.previewBusyModal {
+  display: grid;
+  justify-items: center;
+  gap: 10px;
+  color: var(--text1);
+  text-align: center;
+}
+
+.previewBusyText {
+  font-size: var(--text-xs);
+  font-weight: 700;
+  color: rgba(255, 255, 255, 0.92);
+}
+
+.previewSpinner {
+  width: 26px;
+  height: 26px;
+  border-radius: 999px;
+  border: 3px solid rgba(255, 255, 255, 0.25);
+  border-top-color: rgba(255, 255, 255, 0.9);
+  animation: previewSpin 0.9s linear infinite;
+}
+
+@keyframes previewSpin {
+  to {
+    transform: rotate(360deg);
+  }
 }
 
 .videoCover {