Use one UI drop shadow for text and atlas images, fix Windows build

Text and the SVG button images are mixed on screen, so they now share
UIDropShadowParams (3 UI units of blur, 0.66 intensity, no offset, the
atlas's existing look) instead of the text having its own.

draw_text.cpp included <windows.h> directly, whose min/max macros broke
the std::max calls added here. Include CommonWindows.h instead.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

unittest/UnitTest.cpp

@@ -3697,7 +3697,7 @@ bool TestTextDrawerCache() {
 	EXPECT_EQ_INT((int)bitmap.size(), entry1.bmWidth * entry1.bmHeight * 4);
 	const uint32_t *pixels = (const uint32_t *)bitmap.data();
 	auto pixel = [&](int x, int y) { return pixels[(y + pad) * entry1.bmWidth + x + pad]; };
-	// The text stays opaque white, the shadow is black and partly transparent below-right of it, and the far corner is empty.
+	// The text stays opaque white, the shadow around it is black and partly transparent, and the far corner is empty.
 	EXPECT_EQ_INT(pixel(8, 8), 0xFFFFFFFF);
 	EXPECT_EQ_INT(pixel(12, 12) & 0x00FFFFFF, 0);
 	EXPECT_TRUE((pixel(12, 12) >> 24) > 0);
@@ -3708,7 +3708,7 @@ bool TestTextDrawerCache() {
 	return true;
 }
 
-// The atlas shadow has no offset, so it pads the image evenly and stays symmetric around it.
+// The UI shadow has no offset, so it pads the image evenly and stays symmetric around it.
 bool TestAtlasDropShadow() {
 	Image img;
 	img.scale = 2.0f;
@@ -3718,7 +3718,7 @@ bool TestAtlasDropShadow() {
 			img.set1(x, y, 0xFFFFFFFF);
 		}
 	}
-	AddDropShadow(img, 3, 0.66f);
+	AddDropShadow(img, UIDropShadowParams(img.scale));
 	EXPECT_EQ_INT(img.w, 8 + 12);
 	EXPECT_EQ_INT(img.h, 8 + 12);
 	EXPECT_EQ_HEX(img.get1(6 + 3, 6 + 3), 0xFFFFFFFF);