ISTANBUL Israeli army forces staged an incursion into a strategic area in southern Lebanon on Thursday, in the latest violation of a cease-fire agreement, Lebanese media said.   Israeli forces moved into the Wadi al-Hujeir area, firing heavy-caliber machineguns during their advance in the region, the state news agency NNA reported.  The Lebanese army closed all roads leading to the area after the sudden Israeli incursion, the broadcaster said.  The Israeli raid has forced residents of the