Add HP and SmartBot; refactor bots and World

Introduce health (hp) and damage handling to Robot/BaseRobot
interfaces. Add SmartBot implementation. Refactor bot mining and
movement to use new World APIs (mine, mineAllPositive,
sortPositiveValues). Simplify RandomBot, DigDeepBot, and SortBot
logic, rename/overhaul World rearrange/display, and fix several
indexing/logic bugs and minor cleanups.

include/RandomBot.h

@@ -9,7 +9,4 @@ class RandomBot : public BaseRobot {
   public:
     RandomBot ( int startX, int startY );
     int mine ( World &world ) override;
-
-  private:
-    int randomNumber ();
 };