Refactor inventory unequip logic to use item ID instead of equip target; update README for inventory and skill tree progress

Controllers/InventoryController.cs

@@ -62,12 +62,12 @@ namespace PetCompanion.Controllers
             }
         }
 
-        [HttpPut("{petId}/{equipTarget}/unequip")]
-        public IActionResult UnequipItem(string petId, ItemEquipTarget equipTarget)
+        [HttpPut("{petId}/{itemId}/unequip")]
+        public IActionResult UnequipItem(string petId, int itemId)
         {
             try
             {
-                var updatedPet = inventoryService.UnequipItem(petId, userId.ToString(), equipTarget);
+                var updatedPet = inventoryService.UnequipItem(petId, userId.ToString(), itemId);
                 return Ok(updatedPet);
             }
             catch (Exception ex)