feat: Add shop system, befriend command, and level system

- Added configurable shop system with shop.json
- Created ShopManager class for modular shop handling
- Implemented level system with levels.json for difficulty scaling
- Added multiple duck spawn messages with random selection
- Enhanced message system with color placeholders
- Added ducks_befriended tracking separate from ducks_shot
- Updated help system and admin commands
- All systems tested and working correctly

shop.json

@@ -0,0 +1,25 @@
+{
+  "items": {
+    "1": {
+      "name": "Single Bullet",
+      "price": 5,
+      "description": "1 extra bullet",
+      "type": "ammo",
+      "amount": 1
+    },
+    "2": {
+      "name": "Accuracy Boost",
+      "price": 20,
+      "description": "+10% accuracy",
+      "type": "accuracy",
+      "amount": 10
+    },
+    "3": {
+      "name": "Lucky Charm",
+      "price": 30,
+      "description": "+5% duck spawn chance",
+      "type": "luck",
+      "amount": 5
+    }
+  }
+}