float the build buttons as a horizontal bar over the game world and show key bindings inside build buttons

src/ui/InputMapper.cpp

@@ -51,6 +51,29 @@ std::optional<BuildingType> buildHotkeyType(int digit, bool shiftHeld)
 
 }  // namespace
 
+QString InputMapper::getBuildHotkeyLabel(BuildingType type)
+{
+    // Searched out of the binding table above rather than spelled out a second time,
+    // so a badge can never claim a key the handler does not act on. The shift glyph
+    // is written as a code point because the sources are not guaranteed to be read
+    // as UTF-8 by every compiler this builds with. A plain stroke arrow rather than
+    // U+21E7 UPWARDS WHITE ARROW: the standard UI fonts do not all carry the outlined
+    // shift glyph, and the substitute they fall back to is unreadable at badge size.
+    const QChar shiftGlyph(0x2191);  // U+2191 UPWARDS ARROW
+    for (int digit = 1; digit <= 9; ++digit)
+    {
+        if (buildHotkeyType(digit, false) == type)
+        {
+            return QString::number(digit);
+        }
+        if (buildHotkeyType(digit, true) == type)
+        {
+            return shiftGlyph + QString::number(digit);
+        }
+    }
+    return QString();
+}
+
 bool InputMapper::handleKeyPress(QKeyEvent* event)
 {
     // Auto-repeat says nothing new about which keys are down, and a held action is