refactor: address Copilot review feedback

1. Use MAKELPARAM instead of static_cast for WM_INITMENUPOPUP lParam
   to explicitly match the Windows message contract (LOWORD=position,
   HIWORD=system menu flag).

2. Add init_popup_lparam parameter to construct_with_hmenu to avoid
   sending WM_INITMENUPOPUP twice with conflicting lParam values.
   Previously, the submenu lambda sent WM_INITMENUPOPUP with the
   correct position index, but then construct_with_hmenu would
   immediately resend it with 0xFFFFFFFF, overriding the correct
   value. Now the position is passed through the parameter and sent
   only once inside construct_with_hmenu.

Author: lidaixingchen

src/shell/contextmenu/contextmenu.cc

@@ -135,7 +135,8 @@ std::vector<std::string> extract_hotkeys(const std::string &name) {
 
 menu menu::construct_with_hmenu(
     HMENU hMenu, HWND hWnd, bool is_top,
-    std::function<void(int, WPARAM, LPARAM)> HandleMenuMsg) {
+    std::function<void(int, WPARAM, LPARAM)> HandleMenuMsg,
+    LPARAM init_popup_lparam) {
     menu m;
 
     if (!HandleMenuMsg)
@@ -144,7 +145,7 @@ menu menu::construct_with_hmenu(
         };
 
     HandleMenuMsg(WM_INITMENUPOPUP, reinterpret_cast<WPARAM>(hMenu),
-                  0xFFFFFFFF);
+                  init_popup_lparam);
     for (int i = 0; i < GetMenuItemCount(hMenu); i++) {
         menu_item item;
         wchar_t buffer[256];
@@ -180,11 +181,9 @@ menu menu::construct_with_hmenu(
             int submenu_pos = i;
             item.submenu = [=](std::shared_ptr<menu_widget> mw) {
                 auto task = [&]() {
-                    HandleMenuMsg(WM_INITMENUPOPUP,
-                                  reinterpret_cast<WPARAM>(info.hSubMenu),
-                                  static_cast<LPARAM>(submenu_pos));
                     mw->init_from_data(menu::construct_with_hmenu(
-                        info.hSubMenu, hWnd, false, HandleMenuMsg));
+                        info.hSubMenu, hWnd, false, HandleMenuMsg,
+                        MAKELPARAM(static_cast<WORD>(submenu_pos), 0)));
                 };
                 if (main_thread_id == GetCurrentThreadId())
                     task();

src/shell/contextmenu/contextmenu.h

@@ -20,11 +20,9 @@ struct menu {
 
     static menu
     construct_with_hmenu(HMENU hMenu, HWND hWnd, bool is_top = true,
-                         // This is for handling submenus; messages are required
-                         // to be forwarded to IContextMenu2::HandleMenuMsg for
-                         // submenus and owner-draw menus to work properly
                          std::function<void(int, WPARAM, LPARAM)>
-                             HandleMenuMsg = {});
+                             HandleMenuMsg = {},
+                         LPARAM init_popup_lparam = 0xFFFFFFFF);
 };
 
 std::optional<int>