add restart button to game over screen

src/lib/sim/Simulation.h

@@ -29,6 +29,9 @@ public:
     explicit Simulation(const GameConfig& config, unsigned int seed = 0);
     ~Simulation();
 
+    // Reinitializes all simulation state as if constructed fresh.
+    void reset(unsigned int seed = 0);
+
     // Advances the simulation by one tick. Tick order per architecture.md §Tick Order.
     void tick();