dedupe tunnel lookup and key tunnel tiles by QPoint

The identical 7-line TunnelLookup lambda existed in updateTunnelGhost and
drawSelectedTunnelConnections; it is now GameWorldView::makeTunnelLookup.
The tile key moved from std::pair<int, int> to QPoint with the existing
QPointCompare comparator, dropping the manual packing at every site.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GH8ZMRY3vhxxXcaUxBqxkk

src/ui/GameWorldView.h

@@ -67,6 +67,9 @@ struct QPointCompare
     }
 };
 
+// Tunnel entries/exits indexed by their single-cell tile (REQ-BLD-TUNNEL-MODE).
+using TunnelTileMap = std::map<QPoint, TunnelTileInfo, QPointCompare>;
+
 class GameWorldView : public QOpenGLWidget,
                       public CombinedEventHandler<BeamFiredEvent,
                                                   BuildingTypeSelectedEvent,
@@ -242,7 +245,10 @@ private:
     void         updateTunnelGhost();
     // Indexes every tunnel entry/exit — built or still a construction site — by its
     // single-cell tile. Shared by the placement preview and the selection highlight.
-    std::map<std::pair<int, int>, TunnelTileInfo> collectTunnelTiles() const;
+    TunnelTileMap collectTunnelTiles() const;
+    // Wraps a tunnel tile index in the lookup functor the TunnelCompletion helpers
+    // take. The returned functor references `tunnels`, which must outlive it.
+    static TunnelLookup makeTunnelLookup(const TunnelTileMap& tunnels);
     // Draws the green connection highlight for every selected tunnel end that has a
     // matching end (REQ-BLD-TUNNEL-SELECT-HIGHLIGHT).
     void         drawSelectedTunnelConnections(QPainter& painter);