Papercut build

Build every episode on the library instead of writing a Remotion project from scratch. Read library/README.md once.

Preflight

• Install: Standard or Full. Needs the library, node 20+, npm, ffmpeg, Python tools (numpy, Pillow, soundfile) and Chrome or Chromium for the audio render. Probe with the commands in papercut-explainer; if something is missing, run ./install.sh --doctor and hand over to papercut-setup.
• Library: $PAPERCUT_LIB, else the PAPERCUT_LIB= line in ~/.config/papercut-explainer/config.env, else ask once. With no library at all, build from the sketches in ../papercut-explainer/references/remotion-recipes.md.
• Load the Remotion best-practices skill first (remotion-best-practices, from the Remotion plugin, or npx skills add remotion-dev/skills -g -y -a <your harness id>; install.sh --mode standard does this) and follow its routing for markup, captions and the Studio.
• Needs papercut/STORYBOARD.md and narration/script.json from the earlier stages.
• Smoke test of the whole toolchain: library/tools/selftest.sh builds examples/hello-reel/ in a throwaway folder and renders one still.

1. Scaffold

$PAPERCUT_LIB/new_episode.sh <series-dir> NN-slug CompId [out-name]

It creates <series>/episodes/NN-slug/{research,narration/voice,papercut} with the template project and a synced copy of the kit in src/lib/. node_modules comes from $DONOR, else the newest sibling episode, else npm i. If <series>/papercut-assets/ exists, it is laid over the default textures and props.