Implement real MsgBox() for VBScript table scripts (browser confirm/alert)

libwinevbs's __LIBWINEVBS__ build of Global_MsgBox() only logged the
prompt text and never set a return value, since it has no host UI to
show a dialog through. Any table script that branches on
MsgBox(...) = vbYes (a common pattern - e.g. core.vbs's own trough
ball-count dialog) always took the "no" branch, since the result
stayed at its zero-initialized default.

Adds a msgbox callback to libwinevbs_callbacks_t, wired on the
vpinball-wasm side to a real window.confirm()/alert() call. Both are
synchronous browser APIs that block JS execution and return a value
immediately, matching what VBScript's MsgBox() needs (its result is
used by the calling statement right away) - the only way to answer it
asynchronously would require Asyncify or a busy-wait poll loop, which
this project has deliberately avoided elsewhere.

Confirmed fixed by hands-on testing: a table's ball-count confirm
dialog now correctly returns Yes/No based on the user's click, instead
of always silently taking the "no" branch.

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

patches/libwinevbs/0002-msgbox-callback.patch

@@ -0,0 +1,64 @@
+diff --git a/include/libwinevbs.h b/include/libwinevbs.h
+index 3ba4df9..6cac7df 100644
+--- a/include/libwinevbs.h
++++ b/include/libwinevbs.h
+@@ -52,6 +52,14 @@ LIBWINEVBS_API const char* libwinevbs_hresult_name(HRESULT hr);
+ typedef struct {
+    void (*log)(libwinevbs_log_level_t level, const char* format, va_list args);
+    HRESULT (*create_object)(const WCHAR* progid, IClassFactory* cf, IUnknown** obj);
++   /* Answers a VBScript MsgBox() call. Must return synchronously (its result
++      is used by the calling script statement immediately) - e.g. a real,
++      blocking confirm()/alert() call under Emscripten. type is the raw
++      VBScript "buttons" argument (MB_OK=0, MB_OKCANCEL=1, MB_YESNO=4, ...);
++      title may be NULL. Return the matching button id (IDOK=1, IDCANCEL=2,
++      IDABORT=3, IDRETRY=4, IDIGNORE=5, IDYES=6, IDNO=7), matching vbOK..vbNo.
++      If unset, MsgBox always answers IDOK/vbOK without asking anything. */
++   int (*msgbox)(const char* prompt, int type, const char* title);
+ } libwinevbs_callbacks_t;
+ 
+ LIBWINEVBS_API void libwinevbs_init(const libwinevbs_callbacks_t* callbacks);
+diff --git a/src/libwinevbs.c b/src/libwinevbs.c
+index 7b3d6f0..91091e4 100644
+--- a/src/libwinevbs.c
++++ b/src/libwinevbs.c
+@@ -32,6 +32,14 @@ HRESULT libwinevbs_create_object(const WCHAR* progid, IClassFactory* cf, IUnknow
+    return CLASS_E_CLASSNOTAVAILABLE;
+ }
+ 
++int libwinevbs_msgbox(const char* prompt, int type, const char* title)
++{
++   if (g_callbacks.msgbox)
++      return g_callbacks.msgbox(prompt, type, title);
++
++   return 1; /* IDOK/vbOK - no host callback registered, so just proceed */
++}
++
+ const char* libwinevbs_hresult_name(HRESULT hr)
+ {
+    switch (hr) {
+diff --git a/wine/dlls/vbscript/global.c b/wine/dlls/vbscript/global.c
+index 0e0e144..351f967 100644
+--- a/wine/dlls/vbscript/global.c
++++ b/wine/dlls/vbscript/global.c
+@@ -33,6 +33,7 @@
+ #include <locale.h>
+ #include "scrrun_private.h"
+ HRESULT libwinevbs_create_object(const WCHAR *progid, IClassFactory* cf, IUnknown** obj);
++int libwinevbs_msgbox(const char *prompt, int type, const char *title);
+ extern HRESULT WINAPI WshShellFactory_CreateInstance(IClassFactory*,IUnknown*,REFIID,void**);
+ #endif
+ 
+@@ -2834,9 +2835,12 @@ static HRESULT Global_MsgBox(BuiltinDisp *This, VARIANT *args, unsigned args_cnt
+         hres = show_msgbox(This->ctx, prompt, type, title, res);
+ #else
+     if(SUCCEEDED(hres)) {
+-        char buf[2048];
++        char buf[2048], title_buf[256] = {0};
+         WideCharToMultiByte(CP_ACP, 0, prompt, -1, buf, sizeof(buf) - 1, NULL, NULL);
++        if (title)
++            WideCharToMultiByte(CP_ACP, 0, title, -1, title_buf, sizeof(title_buf) - 1, NULL, NULL);
+         libwinevbs_log(LIBWINEVBS_LOG_INFO, "vbscript: MsgBox prompt=%s", buf);
++        hres = return_short(res, libwinevbs_msgbox(buf, type, title ? title_buf : NULL));
+     }
+ #endif
+