feat: implement item durability tracking and vendor repair

- Add ITEM_FIELD_DURABILITY (60) and ITEM_FIELD_MAXDURABILITY (61) to
  update_field_table.hpp enum and wotlk/update_fields.json
- Add curDurability/maxDurability to OnlineItemInfo and ItemDef structs
- Parse durability fields in OBJECT_CREATE and OBJECT_VALUES handlers;
  preserve existing values on partial updates (fixes stale durability
  being reset to 0 on stack-count-only updates)
- Propagate durability to ItemDef in all 5 rebuildOnlineInventory() paths
- Implement GameHandler::repairItem() and repairAll() via CMSG_REPAIR_ITEM
  (itemGuid=0 repairs all equipped items per WotLK protocol)
- Add canRepair flag to ListInventoryData; set it when player selects
  GOSSIP_OPTION_ARMORER in gossip window
- Show "Repair All" button in vendor window header when canRepair=true
- Display color-coded durability in item tooltip (green >50%, yellow
  >25%, red <=25%)

include/game/world_packets.hpp

@@ -2179,6 +2179,7 @@ struct VendorItem {
 struct ListInventoryData {
     uint64_t vendorGuid = 0;
     std::vector<VendorItem> items;
+    bool canRepair = false;  // Set when vendor was opened via GOSSIP_OPTION_ARMORER
 
     bool isValid() const { return true; }
 };