[ZoomIt] Theme-aware system-tray menu + reusable helper

Makes ZoomIt's system-tray context menu follow the OS light/dark theme,
including live theme switches, and factors the logic into a small reusable
helper that any PowerToys system-tray utility can adopt.

src/common/Themes/dark_menu.h (header-only):
  - SetAppMode(bool dark): render this process's popup menus dark or light.
  - IsSystemDarkMode(): current app theme via the documented AppsUseLightTheme
    value, read fresh so a live light<->dark switch is reflected.
Drop-in for any Win32 tray utility:
  theme::dark_menu::SetAppMode(theme::dark_menu::IsSystemDarkMode());
  TrackPopupMenu(menu, ...);

ZoomIt (first adopter): the tray menu now follows Light/Dark and updates live
on a theme switch without restarting. The OS renders the real themed menu, so
native keyboard, accessibility, checkmarks, separators and DPI are preserved --
only the colors change. The standalone (non-PowerToys) build is unchanged,
under the existing __ZOOMIT_POWERTOYS__ guard.

Testing: MSBuild src\modules\ZoomIt\ZoomIt\ZoomIt.vcxproj /p:Configuration=Release
/p:Platform=x64 /m -- 0 warnings, 0 errors. Verified Light, Dark, and a live
theme switch on Windows 11.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/common/Themes/Themes.vcxproj

@@ -30,6 +30,7 @@
     </ClCompile>
   </ItemDefinitionGroup>
   <ItemGroup>
+    <ClInclude Include="dark_menu.h" />
     <ClInclude Include="icon_helpers.h" />
     <ClInclude Include="theme_listener.h" />
     <ClInclude Include="theme_helpers.h" />

src/common/Themes/dark_menu.h

@@ -0,0 +1,97 @@
+// Theme-aware rendering for classic Win32 popup menus (HMENU / TrackPopupMenu).
+//
+// Lets a Win32 tray/popup menu follow the OS light/dark theme. It puts the
+// process into the matching app theme via uxtheme's preferred-app-mode entry
+// points -- the same mechanism the OS uses to render dark menus, as already
+// used by ZoomIt and File Explorer -- and then the system draws the real
+// themed menu. Native keyboard, accessibility, checkmarks, separators and DPI
+// are all preserved; only the colors change.
+//
+// Theme detection reads the documented AppsUseLightTheme value, fresh on each
+// call, so a live light<->dark switch is reflected without restarting.
+//
+// Drop-in for any PowerToys system-tray utility:
+//
+//     theme::dark_menu::SetAppMode(theme::dark_menu::IsSystemDarkMode());
+//     TrackPopupMenu(menu, ...);
+#pragma once
+
+#include <windows.h>
+
+namespace theme::dark_menu
+{
+    namespace details
+    {
+        // uxtheme preferred-app-mode values (order matters).
+        enum class PreferredAppMode
+        {
+            Default = 0,
+            AllowDark,
+            ForceDark,
+            ForceLight,
+            Max
+        };
+
+        using SetPreferredAppModeFn = PreferredAppMode(WINAPI*)(PreferredAppMode);
+        using FlushMenuThemesFn = void(WINAPI*)();
+
+        struct Ordinals
+        {
+            SetPreferredAppModeFn setPreferredAppMode = nullptr;
+            FlushMenuThemesFn flushMenuThemes = nullptr;
+        };
+
+        // Resolved once per process: an inline function's local static is a single
+        // shared instance across all translation units that include this header.
+        inline const Ordinals& GetOrdinals() noexcept
+        {
+            static const Ordinals ordinals = []() noexcept {
+                Ordinals result{};
+                HMODULE uxtheme = GetModuleHandleW(L"uxtheme.dll");
+                if (uxtheme == nullptr)
+                {
+                    uxtheme = LoadLibraryExW(L"uxtheme.dll", nullptr, LOAD_LIBRARY_SEARCH_SYSTEM32);
+                }
+                if (uxtheme != nullptr)
+                {
+                    // Ordinal 135 = SetPreferredAppMode, ordinal 136 = FlushMenuThemes.
+                    result.setPreferredAppMode = reinterpret_cast<SetPreferredAppModeFn>(
+                        GetProcAddress(uxtheme, MAKEINTRESOURCEA(135)));
+                    result.flushMenuThemes = reinterpret_cast<FlushMenuThemesFn>(
+                        GetProcAddress(uxtheme, MAKEINTRESOURCEA(136)));
+                }
+                return result;
+            }();
+            return ordinals;
+        }
+    }
+
+    // True if the user's app theme is dark, via the documented AppsUseLightTheme value.
+    inline bool IsSystemDarkMode() noexcept
+    {
+        DWORD value = 1; // default to light if the value is missing
+        DWORD size = sizeof(value);
+        RegGetValueW(HKEY_CURRENT_USER,
+                     L"Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize",
+                     L"AppsUseLightTheme", RRF_RT_REG_DWORD, nullptr, &value, &size);
+        return value == 0;
+    }
+
+    // Make this process's classic popup menus render dark or light. Cheap and
+    // idempotent -- call right before TrackPopupMenu so the menu always matches
+    // the current theme, including after a live theme switch. No-op if those
+    // entry points are unavailable.
+    inline void SetAppMode(bool dark) noexcept
+    {
+        const details::Ordinals& ordinals = details::GetOrdinals();
+        if (ordinals.setPreferredAppMode != nullptr)
+        {
+            ordinals.setPreferredAppMode(dark ? details::PreferredAppMode::ForceDark
+                                              : details::PreferredAppMode::ForceLight);
+        }
+        if (ordinals.flushMenuThemes != nullptr)
+        {
+            ordinals.flushMenuThemes();
+        }
+    }
+}

src/modules/ZoomIt/ZoomIt/Zoomit.cpp

@@ -34,6 +34,7 @@
 #include <common/utils/logger_helper.h>
 #include <common/utils/winapi_error.h>
 #include <common/utils/gpo.h>
+#include <common/Themes/dark_menu.h>
 #include <array>
 #include <vector>
 #endif // __ZOOMIT_POWERTOYS__
@@ -10163,8 +10164,23 @@ LRESULT APIENTRY MainWndProc(
                 InsertMenu( hPopupMenu, 0, MF_BYPOSITION|MF_SEPARATOR, 0, NULL );
                 InsertMenu( hPopupMenu, 0, MF_BYPOSITION, IDC_OPTIONS, L"&Options" );
             }
-            // Apply dark mode theme to the menu
+            // Make the popup theme-aware (dark/light).
+#ifdef __ZOOMIT_POWERTOYS__
+            // Shared common helper: the OS renders the dark/light menu (native
+            // chrome, keyboard, accessibility). Reusable by other Win32 modules
+            // such as the runner tray menu.
+            //
+            // Detect the theme fresh at open time (respecting ZoomIt's theme
+            // override) so a live light<->dark switch is reflected without a
+            // restart. IsDarkModeEnabled() uses uxtheme's cached state, which a
+            // runtime theme switch may not refresh, whereas the AppsUseLightTheme
+            // registry value (read by IsSystemDarkMode) is always current.
+            const bool useDarkMenu = ( g_ThemeOverride == 1 ) ||
+                                     ( g_ThemeOverride != 0 && theme::dark_menu::IsSystemDarkMode() );
+            theme::dark_menu::SetAppMode( useDarkMenu );
+#else
             ApplyDarkModeToMenu( hPopupMenu );
+#endif
             TrackPopupMenu( hPopupMenu, 0, pt.x , pt.y, 0, hWnd, NULL );
             DestroyMenu( hPopupMenu );
             break;