fix(platform): decode GDI ANSI text with the font charset's code page

TextOutA / GetTextExtentPoint32A in the Win32 GDI shim always decoded with CP_ACP (1252), so the
server notices drawn by uiTip.TipBoard / BigBoard (CTextBar, a GB2312_CHARSET font in the 936
locale) showed GBK bytes as Latin-1 mojibake. Windows GDI decodes ANSI calls with the code page of
the selected font's charset; the shim now keeps lfCharSet on the font and does the same.
port.text_bar checks TextOutA of GBK bytes against TextOutW of the Unicode text, and the extent.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/port/port_text_bar_test.cpp

@@ -13,6 +13,8 @@
 #include <cmath>
 #include <cstdio>
 #include <cstdlib>
+#include <cstring>
+#include <cwchar>
 #include <string>
 #include <vector>
 
@@ -60,6 +62,39 @@ static int opaque_pixels(const std::string& name, std::uint32_t* sample)
 	return count;
 }
 
+// Renders text into a 64 x 20 DIB with a 12 px font of the given charset (A or W call); returns the bits.
+static std::vector<std::uint32_t> gdi_text(BYTE charset, const char* ansi, const wchar_t* wide)
+{
+	BITMAPINFO info = {};
+	info.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
+	info.bmiHeader.biWidth = 64;
+	info.bmiHeader.biHeight = -20;
+	info.bmiHeader.biPlanes = 1;
+	info.bmiHeader.biBitCount = 32;
+	void* bits = NULL;
+	HDC dc = CreateCompatibleDC(NULL);
+	HBITMAP bmp = CreateDIBSection(dc, &info, DIB_RGB_COLORS, &bits, NULL, 0);
+	SelectObject(dc, bmp);
+	LOGFONT lf = {};
+	lf.lfHeight = 12;
+	lf.lfCharSet = charset;
+	lf.lfQuality = ANTIALIASED_QUALITY;
+	std::strcpy(lf.lfFaceName, "Arial");
+	HFONT font = CreateFontIndirect(&lf);
+	SelectObject(dc, font);
+	SetBkMode(dc, TRANSPARENT);
+	SetTextColor(dc, RGB(255, 255, 255));
+	if (ansi)
+		TextOutA(dc, 0, 0, ansi, int(std::strlen(ansi)));
+	else
+		TextOutW(dc, 0, 0, wide, int(std::wcslen(wide)));
+	std::vector<std::uint32_t> out(static_cast<std::uint32_t*>(bits), static_cast<std::uint32_t*>(bits) + 64 * 20);
+	DeleteObject(font);
+	DeleteDC(dc);
+	DeleteObject(bmp);
+	return out;
+}
+
 static bool near(float a, float b)
 {
 	return std::fabs(a - b) < 1e-3f;
@@ -162,6 +197,28 @@ int main()
 		CHECK(images().size() == 1);	// 64 x 64 fits in one block (count 0, rest 64)
 	}
 
+	{
+		// GDI's ANSI calls decode with the selected font's charset (CTextBar: GetCharsetFromCodePage of the
+		// locale), so a 936 server notice in GBK draws as the CJK text, not as its bytes read as CP 1252.
+		const char gbk[] = "\xB9\xAB\xB8\xE6";	// "公告"
+		const std::vector<std::uint32_t> wide = gdi_text(GB2312_CHARSET, NULL, L"\u516C\u544A");
+		int lit = 0;
+		for (std::uint32_t px : wide)
+			lit += px != 0;
+		CHECK(lit > 20);
+		CHECK(gdi_text(GB2312_CHARSET, gbk, NULL) == wide);
+		CHECK(gdi_text(ANSI_CHARSET, gbk, NULL) != wide);
+		SIZE size = {};
+		SetDefaultCodePage(936);
+		CTextBar bar(12, false);
+		CHECK(bar.Create(NULL, 64, 20));
+		bar.GetTextExtent(gbk, &size);
+		SIZE one = {};
+		bar.GetTextExtent("\xB9\xAB", &one);
+		CHECK(one.cx > 0 && size.cx == 2 * one.cx);	// two full-width glyphs, not four Latin-1 ones
+		SetDefaultCodePage(1252);
+	}
+
 	DeviceAccess::Set(NULL);
 	device->Release();
 	if (!g_failures)