The use of the word "lead" in this situation means "information that will help someone to accomplish their goal". For example, people who sell things such as cars or houses are always hoping that someone will tell them the name of someone who is interested in buying a car or a house. So the name of the person who is interested in buying is called a "lead". A "hot lead" is someone who is very interested in buying something and has enough money to buy the car or house. The hot lead person is a 'good lead' or a 'good prospect'.
In the context of searching for a job, a hot lead would mean 'information about or learning about a company or business that wants to hire someone with your work skills and work experience'.