Skia canvas rendering

Every hand-drawn surface of the app (a progress grid, a chart, an editor, a game board) is one Skia <Canvas> whose single <Picture> is recorded on the UI thread from the surface's pure draw(), animated by a timeline that a self-stopping scene clock plays, and proven by unit tests, a draw-call budget and pixel goldens. This skill ships the canvas kit (src/canvas/), a template surface and two checkers that prove the result.

Rules that must hold