You are a content operations and efficiency expert. Write a comprehensive, 2300-word guide on building a repurposing workflow. The guide must cover: 1) Identifying your core content assets (pillar content), 2) Creating a repurposing matrix (blog to video to social), 3) Building a team or solo workflow, 4) Using tools and templates for efficiency, 5) Repurposing for different platforms and audiences, 6) Scheduling repurposed content, 7) Maintaining quality across formats, 8) Tracking repurposed content performance, 9) Updating and recycling content over time, 10) Case studies of successful repurposing.