Show paper citation counts; add the Paper Surveys type

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Adds a live citation count to paper posts and a new Paper Surveys post type.

Citation count

• New optional front-matter key paper_doi (paper types only). js/citations.js calls the Semantic Scholar Graph API from the browser: arXiv:<id> for 10.48550/arXiv.<id>, DOI:<doi> otherwise.
• The count shows as a "Citations" field at the end of the post meta panel and links to the paper on Semantic Scholar.
• Results are cached per DOI in localStorage for 24h. On 429, network error or the 5s timeout, the last value is shown or the field stays hidden; there are no retries. A count of 0 and a not-found (404) result are hidden too.
• No number is baked into the HTML.
• No CSP exists, so there is nothing to update.

Backfill

• paper_doi was filled on 28 paper posts (every Paper Reviews / Paper Summaries post), from the source paper's arXiv link: the first entry under References, matched against the title, with the version stripped. The key sits right under paper_author.
• Skipped: 0.
• The one-off script was run and not committed.
• Known gaps on Semantic Scholar: Gemini 1 (2312.11805) is not found by arXiv ID, and DeepSeek-V3 (2412.19437) resolves to a duplicate record with 0 citations. Both posts show no field.

Paper Surveys

• A new type for posts that trace one topic through several papers in publication order.
• It has its own /paper-surveys/ page (empty state for now) and a nav tab.
• Seven tabs wrapped the 48em bar, so tabs use a short nav_title (Summaries / Reviews / Surveys) and desktop link padding is 1.1em. The footer site map keeps the full titles.

scholar-lens

Changed keys in _data/post_conventions.yml:

• types.Paper Surveys: {} (new)
• the types comment, which describes paper_doi and Paper Surveys

The scholar-lens copy needs the same change before its drift check passes.

New lint rule in script/lint-posts.rb: on a paper type, paper_doi must be a bare DOI; on any other type it is an error.

Passes:

• "10.48550/arXiv.2310.06825"
• "10.18653/v1/2024.acl-long.1"

Fails:

• "https://doi.org/10.48550/arXiv.2310.06825"
• "arXiv:2310.06825"
• ""
• 10.48550
• "10.1000/a?b"
• "10.1000/a#b"
• any paper_doi on Tech Guides, Insights or Paper Surveys

Verification

• tests: 174 runs, 0 failures
• lint: 35 posts follow the conventions
• strict build, htmlproofer and validate-site.sh all pass
• Playwright, with the API mocked: a 200 response, a reload within 24h (no request), 429 with and without a stale cache, a blocked request, the 5s timeout, light and dark themes, 360–1440px, print, and the aria snapshot
• Two adversarial review rounds (code/tests/docs and UI/UX). Round 2 found 0 MAJOR issues.
• One real API call returned 11,027 for DPO.