Cynthia Littleton Business Editor “The Simpsons” occupies a unique perch in the history of global television. At 36 seasons and 750-plus episodes and counting, the Fox animated franchise been a steady engine of employment for writers, producers, directors, actors and other Hollywood artisans for more than a generation. The show’s legacy was saluted Friday morning with a “Simpsons”-themed Writers Guild of America picket gathering outside Fox Studios that drew dozens of staffers past and present. In the context of labor battles over the future of TV, “The Simpsons” is seen as an example of the kind of employment and the kind of series that is disappearing in the new era.