implement visual feedback for copy building settings with shift + click gesture

src/ui/GameWorldView.h

@@ -117,6 +117,7 @@ private:
     void drawTiles(QPainter& painter);
     void drawBuildings(QPainter& painter);
     void drawSelectionHighlights(QPainter& painter);
+    void drawCopyConfigFeedback(QPainter& painter);
     void drawStations(QPainter& painter);
     void drawBeltItems(QPainter& painter);
     void drawScrap(QPainter& painter);
@@ -138,6 +139,10 @@ private:
     QPoint   widgetToTile(QPoint widgetPt) const;
     QRectF   tileRect(QPoint tile) const;
     QRect    viewportRect() const;
+    // Widget-space rectangle covering a building or construction site's footprint,
+    // or nullopt if the id resolves to neither. Shared by the selection highlight
+    // and the copy-settings feedback (REQ-BLD-COPY-CONFIG-FEEDBACK).
+    std::optional<QRectF> footprintWidgetRect(BuildingId id) const;
 
     float    asteroidLeftEdge() const;
     float    enemyStationRightEdge() const;
@@ -226,6 +231,18 @@ private:
     // only while Shift is down and cleared on Shift release.
     std::optional<BuildingConfig> m_copiedConfig;
 
+    // Brief outline flash shown on a building when settings are copied from it or
+    // pasted onto it (REQ-BLD-COPY-CONFIG-FEEDBACK). remainingMs counts down in
+    // wall-clock time so the flash plays at a fixed length regardless of game speed
+    // (and while paused).
+    struct CopyConfigFlash
+    {
+        BuildingId id;
+        qint64     remainingMs;
+    };
+    std::vector<CopyConfigFlash> m_copyConfigFlashes;
+    static constexpr qint64      kCopyFlashDurationMs = 300;
+
     bool     m_demolishMode;
     BuildingId m_demolishHoverBuildingId;
     bool     m_debugDraw;