fix: enchanter NPC various gossip and enchant bugs

[Boidlz]

• item name showing as %s in enchant notification (SendNotification no longer takes printf args)
• shield block and titanium plating enchants were swapped
• shield block label was wrong (36 instead of actual 15)
• offhand enchant check used INVTYPE_WEAPON, broke for INVTYPE_WEAPONOFFHAND items (fixed with ITEM_CLASS_WEAPON)
• wrong item type or no item equipped opened empty gossip window instead of closing (2h, shield, offhand)