PHILADELPHIA — Hundreds of volunteers gathered at the Girard College gym on a freezing Monday morning to participate in the 29th annual Greater Philadelphia Martin Luther King Day of Service. The participants were a small fraction of the 100,000 people who signed to volunteer in projects throughout the region, according to Global Citizen 365, the organization that hosts the event on the federal holiday marking the civil rights icon’s birthday. “This is more than just a birthday celebration,” said Todd Bernstein, the president of Global Citizen. “It’s an opportunity to embrace Dr. King’s legacy…