papers: register keymaps + hide CV from public index
- Add `arxiv-keymaps` to PAPER_MAP (base=keymaps, slug=keymaps-social-software-26-arxiv).
English source committed; translations will skip until generated.
- Add `hidden: true` flag to PAPER_MAP entries; CV uses it.
Hidden papers still build/deploy (PDF stays accessible by URL) but
are skipped when rendering the public index.
- Drop the live CV row from index.html so the change shows up before
the next oven publish overwrites it.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>