v0.3.0 — zoom-on-callout

New: --zoom (or zoom: true | { factor } in config) smoothly zooms toward each click target and back out — the camera leads the click by a beat, holds through what the click reveals, then releases. Composited in the post phase from callout boxes already in the timing manifest, so it adds nothing to recording time and is fully deterministic. Default factor 1.35.

The attached video is the example tutorial rendered with --zoom. Closes #2.