CLAUDE.md: two new rules

1. ElevenLabs voice only for videos on the site (sharpened existing rule)

Public videos (the site's hero video, anything for obeya.si) are narrated in the owner's ElevenLabs voice clone (…), not the voice of the demo settings. … Credits are limited: only for public videos, … a public video is iterated in local renders …

Videos on the site (the hero video, anything for obeya.si) are narrated in the owner's ElevenLabs voice clone (…), not the voice of the demo settings; demo videos published elsewhere (in a PR or issue comment, say) keep the voice of the demo settings. … Credits are limited: only for the site's videos, … a video for the site is iterated in local renders …

2. Merging an external contributor's pull request (new rule)

Once the owner approves the demo of an external contributor's pull request: comment on the PR with the demo link, squash-merge it, then git pull on main so the local checkout is current.