HUD: centre all UI windows, shift mouse events (not UI commands)

Generic cUI_Window2 hooks centre dialogs, inventory, maps, traders and the
ESC menu. Event shifting now targets the cursor position of mouse events
(move/down/up, x at +8) instead of category 5 UI events, whose +0x48 is not
a point for commands such as opening the ESC menu.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/mods/widescreen.cpp

@@ -65,6 +65,9 @@ int g_renderHeight = 0;
 // Frames from the main menu thread and the loading screen are laid out for
 // 1024x768 ("classic"); everything else is the widened in-game view.
 std::atomic<DWORD> g_menuThread = 0;
+// Whether the most recent scene (on any thread) was a classic one: the main
+// menu is showing. UI input is processed outside the menu thread.
+std::atomic<bool> g_lastSceneClassic = false;
 thread_local int g_loadingScreenDepth = 0;
 
 // D3DVIEWPORT7 (d3d.h is not in current Windows SDKs).
@@ -290,6 +293,10 @@ int RenderWidth() {
     return g_renderWidth;
 }
 
+bool MenuIsShowing() {
+    return g_lastSceneClassic;
+}
+
 bool IsClassicFrame() {
     if (g_renderWidth == 0) {
         return false;
@@ -324,6 +331,9 @@ void __fastcall DxDriver7_LoadingScreen(DxDriver7* self, void* edx, uint32_t pro
 // world the full render size.
 int __fastcall DxDriver7_BeginScene(DxDriver7* self, void* edx) {
     mods::hud::OnDevice(self->device);
+    if (self->sceneDepth == 0) {
+        g_lastSceneClassic = IsClassicFrame();
+    }
     if (g_renderWidth != 0 && self->sceneDepth == 0 && self->device) {
         const bool classic = IsClassicFrame();
         Viewport7 viewport = {0, 0, classic ? 1024u : static_cast<DWORD>(g_renderWidth),