increase scroll speed across contest zone

src/ui/GameWorldView.h

@@ -140,6 +140,8 @@ private:
 
     float    asteroidLeftEdge() const;
     float    enemyStationRightEdge() const;
+    // Horizontal pan speed at a given view-center X, in tiles/s (REQ-UI-SCROLL-SPEED).
+    float    panSpeedTilesPerSecondAt(float viewCenterXTiles) const;
     void     clampScroll();
 
     bool     isValidPlacement(BuildingType type, QPoint anchor, Rotation rot) const;
@@ -179,7 +181,6 @@ private:
     // Beam lifetime in game ticks so beams freeze with the simulation when
     // paused or slowed, instead of fading on wall-clock time (REQ-SHP-FIRING-BEAM).
     static constexpr Tick    kBeamLifetimeTicks      = secondsToTicks(0.3);
-    static constexpr float   kScrollSpeedTilesPerSec = 10.0f;
 
     Simulation*          m_sim;
     const GameConfig*    m_config;