Studio: various panel usability improvements

- Reorder Physics section, move Actuator Groups to end.
- Rename "Physics Settings" → "Physics", "Rendering Settings" → "Rendering".
- Reduce IndentSpacing from 20 to 6.
- Reduce FramePadding Y from 6 to 2 for narrower buttons and popups.
- Remove explicit Unindent/Indent overrides in Rendering and Visibility Groups
  sections so buttons are naturally indented under their tree nodes.
- Dynamically adjust convergence and counts plot X-axis limits based on actual
  solver iterations instead of hardcoded 20.

PiperOrigin-RevId: 906244477
Change-Id: Ic3e6e6e793395158c8cb6692af885884ca3f7f50

src/experimental/studio/app.cc

@@ -1011,14 +1011,14 @@ void App::ModelOptionsGui() {
       ImGuiTreeNodeFlags_SpanAvailWidth | ImGuiTreeNodeFlags_Framed;
 
   ImGui::BeginChild("PhysicsGui", {0, 0}, child_flags);
-  if (ImGui::TreeNodeEx("Physics Settings", node_flags)) {
+  if (ImGui::TreeNodeEx("Physics", node_flags)) {
     platform::PhysicsGui(model(), min_width);
     ImGui::TreePop();
   }
   ImGui::EndChild();
 
   ImGui::BeginChild("RenderingGui", {0, 0}, child_flags);
-  if (ImGui::TreeNodeEx("Rendering Settings", node_flags)) {
+  if (ImGui::TreeNodeEx("Rendering", node_flags)) {
     platform::RenderingGui(model(), &vis_options_, renderer_->GetRenderFlags(),
                            min_width);
     ImGui::TreePop();