Transcript Editor UX Overhaul: Undo/Redo, Section Splitting, and Speaker Navigation

I want a complete overhaul of the transcript editor UX. Specifically, I need: 1. Reliable undo/redo functionality for all editing actions. 2. Precise manual section splitting and speaker reassignment that doesn't cause unwanted changes or reassignments without prompt. 3. Better navigation (jumping around) between speaker sections. 4. A more intuitive experience that doesn't feel like it's fighting the user's manual corrections. It is important because the current experience is incredibly frustrating and makes me not want to use the service.