feat: Add rabbit element with jumping and movement behaviors

This commit introduces a new rabbit element with the following features:
- Jumping mechanics with variable height
- Random direction changes
- Falling and basic ground interaction
- Color variations
- Avoidance of water

The changes include:
- Added RABBIT constant to element types
- Created rabbit.js with updateRabbit function
- Added RABBIT_COLORS to constants
- Implemented basic rabbit movement and behavior logic

js/constants.js

@@ -17,6 +17,7 @@ const FLOWER_COLORS = ['#FF0000', '#FFFF00', '#FF00FF', '#FFA500', '#FFFFFF', '#
 const LEAF_COLOR = '#228B22';
 const FIRE_COLORS = ['#FF0000', '#FF3300', '#FF6600', '#FF9900', '#FFCC00', '#FFFF00'];
 const LAVA_COLORS = ['#FF0000', '#FF3300', '#FF4500', '#FF6600', '#FF8C00'];
+const RABBIT_COLORS = ['#FFFFFF', '#E0E0E0', '#D3C8B4']; // White, Light Gray, Light Brown
 
 // Color variation functions
 function getRandomColorVariation(baseColor, range) {
@@ -58,6 +59,7 @@ const TREE_SEED = 11;
 const LEAF = 12;
 const FIRE = 13;
 const LAVA = 14;
+const RABBIT = 15;
 
 // Flammable materials
 const FLAMMABLE_MATERIALS = [GRASS, WOOD, SEED, GRASS_BLADE, FLOWER, TREE_SEED, LEAF];