Experimental: board videos

talkinghead board and talkinghead board-page render and edit a tablet panel next to the speaker. They are experimental, and the spec format may change before a stable release. board-page opens a browser on port 8765 unless you pass --no-open. The spec is <RUN_DIR>/board/board.json. It holds the tablet recording’s path, an offset that aligns the tablet’s clock with the phone’s, and views (time ranges with a rectangle on the canvas). board renders final-board.mp4 in the run directory. board needs the cut in source order. A restructure cut that moves topic blocks ahead of earlier material is refused with a message.