fix(window): resize the borderless HWND directly so DPI-move sizes are exact

The hardware [WINLOG] trace showed the DPI-transition target computed correctly
(min height 720) but the window stuck ~5% larger (759), with every deferred retry
failing to shrink it. Root cause: the DX11 window is a borderless native HWND
(WS_CAPTION/WS_THICKFRAME, for native move/resize) wrapped by SDL. SDL_SetWindowSize
converts the requested CLIENT size to a window rect via AdjustWindowRectEx (adding
the caption+border frame), but our WM_NCCALCSIZE handler folds that whole frame
back into the client area — so every SDL resize inflates the window by ~one frame
(~39px height, ~16px width) and the 720 minimum becomes an unreachable 759. That,
not the earlier min-ordering/settle logic, is why the height wouldn't stay at min.

resizeWindowExact() resizes the native HWND directly via SetWindowPos on the DX11
path (window rect == client for a borderless window → exact requested size); other
platforms keep SDL_SetWindowSize. Used for the DPI-transition resize and the
deferred retry, so the window now lands on the true minimum in both directions.

Keeps the [WINLOG] native-rect + min-track tracing so the next capture confirms the
fix (or surfaces any remaining gap).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/main.cpp

@@ -578,6 +578,25 @@ static void winlogState(SDL_Window* w, const char* tag)
 #endif
 }
 
+// Resize the window to an EXACT client size. On the DX11 borderless native HWND, SDL_SetWindowSize
+// inflates the result by a phantom caption+border frame: SDL runs AdjustWindowRectEx to turn the
+// requested client size into a window rect (adding the WS_CAPTION/WS_THICKFRAME frame), but our
+// WM_NCCALCSIZE handler folds that entire window rect back into the client area — so the client ends
+// up ~frame bigger than asked (e.g. a 720 min becomes 759, unreachable). Resize the HWND directly:
+// for a borderless window the window rect equals the client, so SetWindowPos gives the exact size.
+static void resizeWindowExact(SDL_Window* window, int w, int h)
+{
+#if defined(_WIN32) && defined(DRAGONX_USE_DX11)
+    HWND hwnd = (HWND)SDL_GetPointerProperty(SDL_GetWindowProperties(window),
+                                             SDL_PROP_WINDOW_WIN32_HWND_POINTER, nullptr);
+    if (hwnd) {
+        SetWindowPos(hwnd, nullptr, 0, 0, w, h, SWP_NOMOVE | SWP_NOZORDER | SWP_NOACTIVATE);
+        return;
+    }
+#endif
+    SDL_SetWindowSize(window, w, h);
+}
+
 // Handle SDL_EVENT_WINDOW_DISPLAY_SCALE_CHANGED: save the old-scale size,
 // compute + clamp the new physical size, arm the deferred resize retry,
 // and rebuild fonts / reset ImGui style at the new DPI scale.  newScale
@@ -662,7 +681,7 @@ static void handleDisplayScaleChange(SDL_Window* window, float newScale,
         // makes the shrink land on the new min immediately, without relying on the deferred retry.
         SDL_SetWindowMinimumSize(window, minW, minH);
         dpiResizePending = true;
-        SDL_SetWindowSize(window, newW, newH);
+        resizeWindowExact(window, newW, newH);
         lastKnownW = newW;
         lastKnownH = newH;
         // Arm deferred retry (SetWindowSize may not stick mid-drag) and suppress resize-recording
@@ -1374,7 +1393,7 @@ int main(int argc, char* argv[])
             SDL_GetWindowSize(window, &curW, &curH);
             if (curW != dpiTargetW || curH != dpiTargetH) {
                 dpiResizePending = true;
-                SDL_SetWindowSize(window, dpiTargetW, dpiTargetH);
+                resizeWindowExact(window, dpiTargetW, dpiTargetH);
                 DEBUG_LOGF("  Deferred resize retry %d: %dx%d -> %dx%d\n",
                        dpiResizeRetries, curW, curH, dpiTargetW, dpiTargetH);
                 winlog("RETRY %d: cur %dx%d != target %dx%d -> SetWindowSize(target)",