Show building_block icon in header stock, expand button and build costs

src/ui/IconCaption.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <QColor>
+#include <QFont>
+#include <QPixmap>
+#include <QString>
+
+// Renders `text` followed by `icon` to its right, vertically centered, onto a
+// transparent pixmap sized to fit both (REQ-UI-BLOCKS-ICON, REQ-UI-BUILD-COST,
+// REQ-UI-EXPAND-BUTTON). Used where a caption must show an inline item icon in
+// place of a trailing word — something QPushButton/QLabel cannot do natively.
+//
+// `textColor` and `font` come from the target widget so the caption stays
+// theme-correct; the result is devicePixelRatio-aware so text and icon stay crisp.
+QPixmap renderCaptionWithIcon(const QString& text, const QPixmap& icon,
+                              const QFont& font, const QColor& textColor);