Require Shift to dock windows

io.ConfigDockingWithShift: plain title-bar/tab drags just move a
window; holding Shift shows the dock-position overlay and docks.

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

src/ui/ImGuiContext.cpp

@@ -94,6 +94,10 @@ bool ImGuiContext::Initialize(const std::string& windowTitle, int width, int hei
     // With NavEnableKeyboard set, io.WantCaptureKeyboard becomes true whenever any
     // ImGui window is focused, which would block all viewport hotkeys (F, A, etc.).
     io.ConfigFlags |= ImGuiConfigFlags_DockingEnable;
+    // Dock only while Shift is held during a title-bar/tab drag (the dock
+    // position overlay appears then); a plain drag just moves the window,
+    // so casual rearranging can't accidentally re-dock panels.
+    io.ConfigDockingWithShift = true;
 
     // Store imgui.ini in %APPDATA%\UsdLayerManager\ so it doesn't litter the CWD.
     if (const char* appData = getenv("APPDATA")) {